Dynex 400 W Power Supply Review
By Gabriel Torres on May 20, 2008


Introduction

Dynex and Rocketfish are two brands owned by Best Buy sold only on their chain of retail stores (and also on their website, of course). Today we are going to review Dynex 400 W, which is a relabeled Huntkey Green Star 400 W power supply and targeted to the entry-level market. Costing USD 80, is it worth the price? Can it really deliver 400 W? Read on.

Dynex and Rocketfish power supplies are manufactured by Huntkey, and we were very curious to review these power supplies from Best Buy for two reasons. First, with more than 1,000 stores worldwide you can find at least one Best Buy store in every major American city. So these power supplies can be found on every corner of the country. Second, we had already reviewed a Huntkey power supply that couldn’t deliver its labeled power, so we were really interested in knowing if that was a problem with that particular model or if all Huntkey models are labeled with a power capacity higher than they can actually deliver.

Dynex 400 W is in fact a relabeled Green Star 400 W and since we had already reviewed the 450 W version from this series – which exploded when we tried to pull its labeled power – we were really curious to know if the all models from Green Star series explode or if this is a problem only with the 450 W model. We were also very curious to see what the internal differences between the 400 W and the 450 W models are.

Dynex 400 W Power Supply
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Figure 1: Dynex 400 W power supply.

Dynex 400 W Power Supply
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Figure 2: Dynex 400 W power supply.

This power supply uses a 120 mm fan on its bottom and it doesn’t come with any PFC circuit.

On Best Buy and Dynex websites the complete specifications for this power supply is missing –they don’t talk about efficiency, for example. On the other hand, the product box and the websites are accurate in describing the available protections (SCP, OCP and OVP). The real problem, however, is Huntkey’s website. They say “85% high efficiency performance,” which is clearly a lie. If you scroll down you can see the correct information, “70% min.” And how about “Support Vista operating system with Direct X 9.0 and Direct X 10 graphic card”? Since when the power supply has something to do with the operating system?

This power supply comes with a 24-pin motherboard cable (it comes with an adapter for you to convert this plug into a 20-pin one), an ATX12V cable and four peripheral cables: one auxiliary power cable for video cards with a 6-pin connector, one cable with three standard peripheral power connectors and one floppy disk drive power connector, one cable with two standard peripheral power connectors and one SATA power connector and one cable with three SATA power plugs.

The number of cables is perfect for entry-level PCs with just one video card or even with on-board video.

This power supply uses 18 AWG and 20 AWG wires. The main motherboard cable, the ATX12V cable and the peripheral cable containing two standard peripheral power connectors and one SATA power connector use 18 AWG wires, while all other cables use 20 AWG wires, including the video card auxiliary power cable. As we always mention, we like to see all wires being 18 AWG.

On the aesthetic side all wires are protected with a nylon sleeving, but this protection doesn’t come from inside the power supply housing.

Now let’s take an in-depth look inside this power supply.

A Look Inside The Dynex 400 W

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

From this first look we could clearly see that Dynex 400 W uses the same design as Huntkey Green Star 450 W. Now we will need to see whether they use the same components or not.

Dynex 400 W Power Supply
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Figure 3: Overall look.

Dynex 400 W Power Supply
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Figure 4: Overall look.

Dynex 400 W Power Supply
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Figure 5: Overall look.

Transient Filtering Stage

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

On this stage this power supply is flawless, providing two extra Y capacitors, one extra X capacitor and one extra coil. This power supply has two MOV’s, located after the rectification bridge. The components used here are identical to the ones used on Huntkey Green Star 450 W.

Dynex 400 W Power Supply
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Figure 6: Transient filtering stage (part 1).

Dynex 400 W Power Supply
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Figure 7: Transient filtering stage (part 2).

Dynex 400 W Power Supply
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Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Dynex 400 W.

Primary Analysis

On this page we will take an in-depth look at the primary stage of Dynex 400 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one RS806 rectifying bridge in its primary, capable of delivering up to 8 A at 100° C. The Green Star 450 W sample we reviewed used a different bridge, D15XB80, which is capable of providing only up to 3.2 A at 25° C if no heatsink is used (installing a heatsink its current limit grows to 15 A). An 8 A bridge is more than enough for a 400 W power supply. The reason why is that at 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Dynex 400 W Power Supply
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Figure 9: Rectifying bridge.

The switching section from Green Star 450 W and from Green Star 400 W (aka Dynex 400 W) is identical. Both are based on the half-bridge design, which is the design usually used when the power supply does not feature active PFC circuit, using regular power NPN transistors instead of MOSFET components. Here two FJP13009 NPN power transistors are used. They can deliver up to 12 A continuous mode or up to 24 A in pulse mode, which is the case. Both values are given at 25° C.

Dynex 400 W Power Supply
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Figure 10: Switching transistors (the second transistor is on the other side of the heatsink).

The switching transistors are controlled by a DM0265R integrated circuit (PWM controller).

Dynex 400 W Power Supply
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Figure 11: PWM controller.

The two electrolytic capacitors used on the voltage doubler are Chinese from Jianghai and rated at 85° C. The capacitors from the Green Star 450 W sample we reviewed were from Teapo, a Taiwanese company.

Secondary Analysis

This power supply uses four Schottky rectifiers on its secondary.

Since this power supply is based on the half-bridge design to calculate the maximum theoretical current/power for each output is easy: we can simply add the maximum current from each diode.

The +12 V output is produced by two MBR20H100CT Schottky rectifiers connected in parallel, which can deliver up to 20 A each (10 A per internal diode, measured at 162° C), thus the maximum theoretical current the +12 V line can deliver is of 40 A, which equals to 480 W. The maximum current this line can really deliver will depend on other components. The Green Star 450 W model we reviewed used different rectifiers, STPS20S100C, but they have the exact same specs from the rectifiers used on this power supply.

The +5 V output is produced by one STPS30S45CW Schottky rectifier, which supports up to 30 A (15 A per internal diode, measured at 135° C). So the maximum theoretical power the +5 V output can deliver is of 150 W. Of course the maximum current (and thus power) this line can really deliver will depend on other components. This is the exact same rectifier used on Green Star 450 W.

The +3.3 V output is produced by another STPS30S45CW Schottky rectifier, which supports up to 30 A (15 A per internal diode, measured at 140° C). So the maximum theoretical power the +3.3 V output can deliver is of 99 W. Of course the maximum current (and thus power) this line can really deliver will depend on other components. This is the exact same rectifier used on Green Star 450 W.

Even though this power supply has a separated rectifier for the +3.3 V output, this rectifier is connected to the same transformer output as the +5 V line, so the maximum current +5 V and +3.3 V can pull together is limited by the transformer.

Dynex 400 W Power Supply
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Figure 12: The four Schottky rectifiers used on the secondary.

This power supply thermal sensor is located close to one of the ends of the secondary heatsink, as you can see in Figure 13. This sensor is used to control the fan speed according to the power supply internal temperature and also to shut the power supply down if it implements over temperature protection (OTP), which isn’t the case of this power supply.

Dynex 400 W Power Supply
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Figure 13: Thermal sensor.

This power supply uses a SG6105 monitoring integrated circuit, which is in charge of the power supply protections. This IC features over voltage protection (OVP), under voltage protection (UVP), short-circuit protection (SCP) and over power protection (OPP). As you can see this IC doesn’t support over current protection (OCP) but Huntkey implemented this protection using a quad-comparator integrated circuit (AS339).

Dynex 400 W Power Supply
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Figure 14: Protection integrated circuits.

Analyzing the printed circuit board we could clearly see each +12 V rail connected to the OCP circuit. Also, each +12 V rail had its own filtering circuit (own coil and own electrolytic capacitor), which is nice to see.

The electrolytic capacitors used on the secondary are from Teapo and Fcon and rated at 105° C.

In summary, Dynex 400 W (Huntkey Green Star 400 W) is IDENTICAL to Huntkey Green Star 450 W.

Power Distribution

In Figure 15, you can see the power supply label containing all the power specs.

Dynex 400 W Power Supply
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Figure 15: Power supply label.

As you can see this power supply has two virtual +12 V rails. As mentioned before we could clearly see on the printed circuit board that each rail was really connected to the over current protection (OCP) circuit, and each one had its own filtering circuit (own coil and own electrolytic capacitor).

Internally Dynex 400 W (Huntkey Green Star 400 W) is IDENTICAL to Huntkey Green Star 450 W. We are not only talking about the design; we are talking about EVERYTHING. So it seems that the 450 W model is just this 400 W unit with a different sticker! Now we are even more curious to take a look at the Green Star 350 W model – will it be the same power supply as well?

Even though they are the exact same power supply, their labels are different. The 400 W model is labeled with lower limits: 14 A for +12V1, 15 A for +12V2, 28 A for +5 V, 30 A for +3.3 V and 0.3 A for -12 V, against 15 A, 17 A, 35 A, 30 A and 0.5 A, respectively, on the 450 W model.

The +12V2 rail is connected only to the ATX12V cable, so everything else is connected to the +12V1 rail.

Now let’s see if this power supply can really deliver 400 W of power.

Load Tests

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.

Usually we test power supplies with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load.

But since we had a bad experience with Huntkey Green Star 450 W (that we now know that internally is identical to this 400 W model), we decided to add one additional load patterns to our methodology, trying to pull around 350 W from this power supply. We also included two load patterns for the 100% load test, one pulling more current from +5 V and +3.3 V outputs than we liked to see (test 6), but respecting more the old project used by this power supply, which uses rectifiers with greater capacity on these outputs, and another representing the current usage of a typical PC (test 7), where we pulled more current from the +12 V outputs.

We broke the results down into two tables. On the first table you see the results for loads between 20% and 80%, and on the second table you see the results for loads between 80% and 100%. Below we will explain more about this second table.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

+12V2 is the second +12V input from our load tester and during our tests it was connected to the power supply ATX12V connector, which is the only thing connected to the unit’s +12V2 rail. So this time +12V1 and +12V2 inputs from our load tester were really connected to the +12V1 and +12V2 rails from the reviewed power supply.

Input

Test 1

Test 2

Test 3

Test 4

+12V1

3 A (36 W)

6 A (72 W)

9 A (108 W)

11 A (132 W)

+12V2

2.5 A (30 W)

6 A (72 W)

8 A (96 W)

11 A (132 W)

+5V

1 A (5 W)

2 A (10 W)

4 A (20 W)

6 A (30 W)

+3.3 V

1 A (3.3 W)

2 A (6.6 W)

4 A (13.2 W)

6 A (19.8 W)

+5VSB

1 A (5 W)

1 A (5 W)

1.5 A (7.5 W)

2 A (10 W)

-12 V

0.3 A (3.6 W)

0.3 A (3.6 W)

0.3 A (3.6 W)

0.3 A (3.6 W)

Total

82.5 W

167.5 W

246.3 W

325.3 W

% Max Load

20.6%

41.9%

61.6%

81.3%

Room Temp.

45.9° C

46.6° C

46.3° C

44.3° C

PSU Temp.

53.9° C

55.4° C

55.2° C

52.1° C

Load Test

Pass

Pass

Pass

Pass

Voltage Stability

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

AC Power (1)

102 W

200 W

298 W

402 W

Efficiency (1)

80.9%

83.8%

82.7%

80.9%

AC Power (2)104.5 W205.9 W306.2 W413.6 W
Efficiency (2)78.9%81.4%80.4%78.7%
AC Voltage111.5 V110.7 V109.9 V109.1 V
Power Factor0.5750.6370.6760.701

Final Result

Pass

Pass

Pass

Pass


Input

Test 5

Test 6

Test 7

+12V1

11 A (132 W)

12 A (144 W)

14 A (168 W)

+12V2

11 A (132 W)

12 A (144 W)

14 A (168 W)

+5V

10 A (50 W)

12 A (60 W)

8 A (40 W)

+3.3 V

10 A (33 W)

12 A (39.6 W)

8 A (26.4 W)

+5VSB

2.5 A (12.5 W)

2.5 A (12.5 W)

2.5 A (12.5 W)

-12 V

0.3 A (3.6 W)

0.3 A (3.6 W)

0.3 A (3.6 W)

Total

364.3 W

406.9 W

402.8 W

% Max Load

91.1%

101.7%

100.7%

Room Temp.

48.1° C

50.1° C

45.5° C

PSU Temp.

58.9° C

62.4° C

54.4° C

Load Test

Pass

Pass

Pass

Voltage Stability

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

AC Power (1)

465 W

536 W

523 W

Efficiency (1)

78.3%

75.9%

77.0%

AC Power (2)477.0 W548.0 W560.0 W
Efficiency (2)76.4%74.3%71.9%
AC Voltage107.9 V107.4 V107.2 V
Power Factor0.7080.7150.718

Final Result

Pass

Pass

Pass

Updated 07/03/2009: We re-tested this power supply using our new GWInsteak GPM-8212 power meter, which is a precision instrument and provides accuracy of 0.2% and thus presenting the correct readings for AC power and efficiency (results marked as "2" on the table above; results marked as "1" were measured with our previous power meter from Brand Electronics, which isn't so precise as you can see). We also added the numbers for AC voltage during our tests, an important number as efficiency is directly proportional to AC voltage (the higher AC voltage is, the higher efficiency is). Also, manufacturers usually announce efficiency at 230 V, which usually inflates efficiency numbers. We added power factor (PF) numbers as well. These numbers measure the efficiency of the power supply active PFC circuit. This number should be as close to 1 as possible. Since this power supply does not feature a PFC circuit, which is in charge of "fixing" the power factor, numbers for this parameter were very low. Units with active PFC achieve numbers above 0.97 here.

The main problem with this power supply is efficiency. You will only see efficiency slightly above 80% when pulling between 40% and 60% from its nominal capacity (between 160 W and 240 W). On all other load patterns efficiency stays below 80%, hitting a hard bottom during test seven, at 71.9%. That is really bad.

Voltage stability, on the other hand, was the highlight of this product, with all outputs between 3% of their nominal voltage in almost all tests, which is excellent (ATX standard allows voltages to be up to 5% from their nominal values – 10% in the case of the -12 V output).  We only saw voltages outside this 3% range on tests one and six on -12 V output, but it was still inside the maximum allowed.

Noise level was far higher than we wanted to see, but still inside ATX specs – actually touching it during test number six, where could see a 113.2 mV noise level at +12V1. Under other patterns – including test seven – noise wasn’t that high, but still at a level far higher than the one achieved by good power supplies. On the other hand, noise level at +3.3 V was always below 15 mV, which is excellent.

We wouldn’t be complaining about noise and efficiency if it was a power supply costing less than USD 40, but for a product that costs the double of that this is simply unacceptable.

The results below are for test number seven.

Dynex 400 W Power Supply
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Figure 16: Noise level at +12V1 with power supply delivering 400 W (81 mV).

Dynex 400 W Power Supply
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Figure 17: Noise level at +12V2 with power supply delivering 400 W (72 mV).


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Figure 18: Noise level at +5 V with power supply delivering 400 W (22 mV).

Dynex 400 W Power Supply
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Figure 19: Noise level at +3.3 V with power supply delivering 400 W (12.2 mV).

Now let’s see if we could pull even more power from this unit and our tests of the power supply protections.

Overload Tests

Before performing our overload tests we always like to test first if the over current protection (OCP) circuit is really active and at what level it is configured.

We configured +12V2 input from our load tester with a low current (1 A) and increased current on +12V1 input (which was connected to the power supply +12V1 rail) until the power shut down. This happened when we tried to pull more than 21 A, so OCP was active and set at 21 A. We think that is a value too far away from what is supposed to be the maximum amount of current this output can deliver.

Then we tried to pull even more power from Dynex 400 W to see what happened. Since this power supply is completely identical to Huntkey Green Star 450 W, we were expecting to explode it when we pulled around 450 W – and, yes, it happened again (third Huntkey Green Star we exploded when pulling around 450 W with the power supply hot).

So we tried several patterns before attempting to go our way to 450 W. The maximum amount of power we could pull from this unit without it exploding was 437.5 W, see the table below.

Input

Maximum

+12V1

17 A (204 W)

+12V2

15 A (180 W)

+5V

6 A (30 W)

+3.3 V

6 A (19.8 W)

+5VSB

2.5 A (12.5 W)

-12 V

0.3 A (3.6 W)

Total

437.5 W

% Max Load

109.4%

Room Temp.

48.6° C

PSU Temp.

60.9° C

Load Test

Pass

Voltage Stability

Pass

Ripple and Noise

Pass

AC Power (1)

616 W

Efficiency (1)

71.0%

Final Result

Pass

Under this load noise level at +12V1 was very high, 105 mV, but still inside ATX specs.

Short circuit protection (SCP) worked fine for both +5 V and +12 V lines.

As a tradition, below you can see the video for this power supply exploding when we pulled around 450 W from it. Keep in mind that when power supplies explode like this it means that the components from the primary were the ones not able to keep up with the amount of power being pulled by the power supply. When the problem is on the secondary (e.g., one of the outputs being overloaded), the power supply dies in silence. In other words, the over power protection (OPP) should have entered in action, what didn’t happen.

 

Main Specifications

Dynex 400 W power supply specs include:

* Researched at BestBuy.com on the day we published this review.

Conclusions

In the old days, low-end Chinese manufacturers had only one power supply model with labels that could be fabricated according to what distributors buying from them wanted to be printed. This kind of power supply is still around – they are the so-called “generic” power supplies, but consumers became aware of this problem and started to demand products with labels that correctly described their current and power limits.

But it seems that Huntkey is still doing that. Dynex 400 W, which is a Huntkey Green Star 400 W, is identical to Huntkey Green Star 450 W: the exact same power supply, different labels describing the maximum currents and power the unit can handle.

This discovery explained why we exploded two Green Star 450 W units when trying to pull 450 W from them: internally they are a Green Star 400 W power supply with a different label. We are now curious to see the internals from other power supplies from the Green Star series like the 350 W and 550 W models to see if they are identical to the 400 W and 450 W models or if the manufacturer upgraded the components according to reflect the new power capacity.

Speaking specifically about Dynex 400 W, the main problem with this power supply is its price. Costing USD 80 it is simply too expensive for a 400 W power supply with low efficiency when delivering between 80% and 100% of its load and with a very high electrical noise level if compared to other good power supplies – even though it was able to deliver its labeled power at 50° C. Not to mention the ridiculous 1-year warranty – all other power supply manufacturers give a warranty of at least three years. Updated 07/03/2009: Best Buy reduced the price for this power supply to USD 49.99. It is still not worth buying it, since it provides efficiency above 80% only when you  pull between 160 W and 240 W from it and it can go as low as 71.9% when you pull 400 W from it.

If you are looking for a cheap power supply for your entry-level PC, Cooler Master eXtreme Real Power Plus 460 W is an excellent choice with its terrific USD 40 price tag. But if you have USD 80 to spend on a power supply, there tons of other better products around costing less than that: SilverStone Strider ST-50F, Corsair VX450W and Zalman ZM-360B-APS, just to name a few.

Originally at http://www.hardwaresecrets.com/article/Dynex-400-W-Power-Supply-Review/557


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