OCZ StealthXStream 400 W Power Supply Review
By Gabriel Torres on August 28, 2009


Introduction

Hardware Secrets Golden Award

StealthXStream 400 W (OCZ400SXS) is an inexpensive entry-level power supply from OCZ, costing only USD 55. Is it a good pick for users building an entry-level or mainstream PC? Let’s check it out.

The reviewed power supply is manufactured by CWT.

OCZ StealthXStream 400 W power supply
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Figure 1: OCZ StealthXStream 400 W power supply.

OCZ StealthXStream 400 W power supply
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Figure 2: OCZ StealthXStream 400 W power supply.

StealthXStream 400 W is 6 19/64” (160 mm) deep, has a 140 mm fan on its bottom, featuring active PFC, of course.

All cables use nylon sleevings, but they don’t come from inside the power supply, as you can see in Figure 2. The included cables are:

The number of cables is perfect for an entry-level or mainstream PC. All cables have 20 7/8” (53 cm) between the power supply housing and the first connector on the cable. On the peripheral power cables there is 5 7/8” (15 cm) between connectors. All wires are 18 AWG, which is the correct gauge to be used.

OCZ StealthXStream 400 W power supply
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Figure 3: Cables.

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

A Look Inside The StealthXStream 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.

OCZ StealthXStream 400 W power supply
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Figure 4: Overall look.

OCZ StealthXStream 400 W power supply
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Figure 5: Overall look.

OCZ StealthXStream 400 W power supply
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Figure 6: 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.

This power supply has all required components, plus two extra Y capacitors, one extra X capacitor and one X capacitor after the rectification bridge.

OCZ StealthXStream 400 W power supply
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Figure 7: Transient filtering stage (part 1).

OCZ StealthXStream 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 OCZ StealthXStream 400 W.

Primary Analysis

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

This power supply uses one KBU10J rectifying bridge in its primary, which can deliver up to 10 A at 100° C, if a heatsink is used, or up to 8 A at 50° C if a heatsink isn’t used, as unfortunately is the case. Nevertheless 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.

OCZ StealthXStream 400 W power supply
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Figure 9: Rectifying bridge.

On the active PFC circuit two STP14NK50ZFP power MOSFET transistors are used, each one capable of delivering up to 14 A at 25° C or 7.6 A at 100° C in continuous mode (note the difference temperature makes) or 48 A in pulse mode at 25° C, presenting a resistance of 380 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is.

OCZ StealthXStream 400 W power supply
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Figure 10: Active PFC transistors and diode.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is Japanese from Rubycon and labeled at 85° C.

In the switching section, another two STP14NK50ZFP power MOSFET transistors are used on the traditional two-transistor forward configuration.

OCZ StealthXStream 400 W power supply
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Figure 11: Switching transistors.

The primary is controlled by a CM6800 PFC/PWM combo controller.

OCZ StealthXStream 400 W power supply
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Figure 12: PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.

Secondary Analysis

This power supply uses four Schottky rectifiers on its secondary.

The maximum theoretical current each line can deliver is given by the formula I / (1 - D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by two SBR30A60CT Schottky rectifiers connected in parallel, each one having a maximum current limit of 30 A (15 A per diode at 110° C, 0.60 V maximum voltage drop). This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output.

The +5 V output is produced by one STPS30L30CT Schottky rectifier, which has a maximum current limit of 30 A (15 A per diode at 140° C, 0.37 V voltage drop), giving us a maximum theoretical current of 21 A or 107 W for this line.

The +3.3 V output is produced by one STPS3045CW Schottky rectifier, which has a maximum current limit of 30 A (15 A per diode at 155° C, 0.57 V voltage drop) giving us a maximum theoretical current of 21 A or 71 W for the +3.3 V output.

OCZ StealthXStream 400 W Power Supply
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Figure 13: One of the +12 V rectifiers and +3.3 V rectifier.

OCZ StealthXStream 400 W Power Supply
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Figure 14: +5 V rectifier and the other +12 V rectifier.

The secondary is monitored by an SG6516DZ integrated circuit, which implements the following protections: overvoltage (OVP), undervoltage (UVP) and overcurrent (OCP).

OCZ StealthXStream 400 W Power Supply
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Figure 15: Monitoring integrated circuit.

Electrolytic capacitors from the secondary are from different vendors: four of them are Japanese from Chemi-Con, but two are Chinese from Samxon and one is Taiwanese from OST.

Power Distribution

In Figure 16, you can see the power supply label containing all the power specs.

OCZ StealthXStream 400 W Power Supply
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Figure 16: Power supply label.

This power supply uses a dual-rail design distributed like this:

This is the typical distribution used on power supplies with two virtual rails.

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

Load Tests

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

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

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.

+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests the +12V1 input was connected to the +12V1 rail the +12V2 input was connected to the +12V2 rail, so on this test +12V1 and +12V2 really represents the rails by the same name on the power supply.

Input

Test 1

Test 2

Test 3

Test 4

Test 5

+12V1

2.5 A (30 W)

5.5 A (66 W)

8 A (96 W)

10.5 A (126 W)

14 A (168 W)

+12V2

2.5 A (30 W)

5.5 A (66 W)

8 A (96 W)

10.5 A (126 W)

13 A (156 W)

+5V

1 A (5 W)

2 A (10 W)

4 A (20 W)

6 A (30 W)

8 A (40 W)

+3.3 V

1 A (3.3 W)

2 A (6.6 W)

4 A (13.2 W)

6 A (19.8 W)

8 A (26.4 W)

+5VSB

1 A (5 W)

1 A (5 W)

1.5 A (7.5 W)

2 A (10 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)

0.3 A (3.6 W)

0.3 A (3.6 W)

Total

77.4 W

157.3 W

236.1 W

314.2 W

402.7 W

% Max Load

19.4%

39.3%

59.0%

78.6%

100.7%

Room Temp.

45.6° C

46.5° C

46.1° C

45.8° C

47.2° C

PSU Temp.

46.5° C

47.5° C

46.6° C

47.1° C

49.3° C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

AC Power

92.0 W

184.4 W

278.1 W

376.0 W

493.7 W

Efficiency

84.1%

85.3%

84.9%

83.6%

81.6%

AC Voltage

112.5 V

112.4 V

110.3 V

109.7 V

109.2 V

Power Factor

0.982

0.99

0.995

0.997

0.998

Final Result

Pass

Pass

Pass

Pass

Pass

OCZ StealthXStream 400 W proved to be one of the best entry-level power supplies we’ve ever tested. It could not only deliver its labeled power at 47° C, but also presented high efficiency, up to 85%. Usually when entry-level products are delivering their labeled wattage efficiency drops below 80%, but this simply didn’t happen with the reviewed power supply.

Voltage stability was another highlight from StealthXStream 400 W, with all outputs always within 3% from their nominal values, i.e., they were closer to their nominal values than required by ATX specification, which allows a tolerance of up to 5% for them. This includes the -12 V output, which traditionally doesn’t like to stay within this tighter limit.

Ripple and noise levels were always very low. Below you can see the results for test number five. The maximums allowed are 120 mV for +12 V and 50 mV for +5 V and +3.3 V. All values are peak-to-peak.

OCZ StealthXStream 400 W Power Supply
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Figure 17: +12V1 rail with the power supply delivering 402.7 W (27.4 mV).

OCZ StealthXStream 400 W Power Supply
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Figure 18: +12V2 rail with the power supply delivering 402.7 W (28.6 mV).

OCZ StealthXStream 400 W Power Supply
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Figure 19: +5 V rail with the power supply delivering 402.7 W (11.6 mV).

OCZ StealthXStream 400 W Power Supply
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Figure 20: +3.3 V rail with the power supply delivering 402.7 W (11.0 mV).

Now let’s see if we could pull more than 400 W from this unit.

Overload Tests

Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured.

In order to do that we increased current on the +12V2 rail until the power supply shut down. This happened when we tried to pull more than 26 A from it.

Manufacturers always leave a margin between what is written on the label (14 A in this case) and the level the OCP circuit is really configured (26 A in this case). We always like to see this margin as tight as possible.

Then starting from test five we increased currents to the maximum we could with the power supply still running inside ATX specs. The results are below. If we tried to increase one amp on any of the outputs a protection would enter in action, shutting down the power supply. Nice.

Input

Maximum

+12V1

15 A (180 W)

+12V2

15 A (180 W)

+5V

10 A (50 W)

+3.3 V

10 A (33 W)

+5VSB

2.5 A (12.5 W)

-12 V

0.3 A (3.6 W)

Total

453.4 W

% Max Load

113.4%

Room Temp.

46.9° C

PSU Temp.

49.8° C

AC Power

566.9 W

Efficiency

80.0%

AC voltage

109.5 V

Power Factor

0.998

Main Specifications

OCZ StealthXStream 400 W power supply specs include:

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

Conclusions

OCZ StealthXStream 400 W is probably the best entry-level power supply we reviewed to date. It can not only deliver its labeled power at 47° C, but also presents a high efficiency of up to 85%, voltages very close to their nominal values (below 3% margin, while ATX spec allows up to 5%) and amazingly low noise and ripple levels.

If you are building an entry-level or mainstream computer with a simple video card, this is one of the best options on the market and its low price (USD 55) makes it to have an unbeatable cost/benefit ratio.

Originally at http://www.hardwaresecrets.com/article/OCZ-StealthXStream-400-W-Power-Supply-Review/794


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