Seasonic X-400 Fanless Power Supply Review

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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 the behavior of the reviewed unit 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. In the “Total” row, we are using the real amount of power being delivered, as measured by our load tester.

The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During our tests, both were connected to the power supply’s single +12 V rail.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 2.5 A (30 W) 5.5 A (66 W) 8 A (96 W) 10.5 A (126 W) 14 A (168 W)
+12VB 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 A (10 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 80.2 W 161.3 W 240.6 W 319.3 W 401.4 W
% Max Load 20.1% 40.3% 60.2% 79.8% 100.4%
Room Temp. 44.8° C 43.2° C 42.2° C 42.4° C 43.8° C
PSU Temp. 59.0° C 58.2° C 58.6° C 58.7° C 59.5° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 91.5 W 176.2 W 263.5 W 352.5 W 449.8 W
Efficiency 87.7% 91.5% 91.3% 90.6% 89.2%
AC Voltage 114.0 V 113.0 V 112.7 V 111.9 V 111
Power Factor 0.969 0.991 0.998 0.988 0.991
Final Result Pass Pass Pass Pass Pass

The Seasonic X-400 Fanless can really deliver its labeled wattage at high temperatures.

Efficiency was extremely high, above 87% at light load (20% load, 80 W) and above 89% at full load, peaking 91.5% at 40% load (160 W). Really impressive.

Voltage regulation was another highlight of this product, with all voltages within 3% of their nominal values – including the -12 V output. The ATX12V specification allows voltages to be up to 5% from their nominal values (10% for the -12 V output). Therefore this power supply presents voltages closer to their nominal values than necessary.

Noise and ripple levels were always extremely low. Below you can see the results for the power supply outputs during test number five. The maximum allowed is 120 mV for +12 V and -12 V outputs, and 50 mV for +5 V and +3.3 V outputs. All values are peak-to-peak figures.

Seasonic X-400 Fanless power supplyFigure 21: +12VA input from load tester during test five at 401.4 W (20.6 mV)

Seasonic X-400 Fanless power supplyFigure 22: +12VB input from load tester during test five at 401.4 W (20.4 mV)

Seasonic X-400 Fanless power supplyFigure 23: +5V rail during test five at 401.4 W (10.2 mV)

Seasonic X-400 Fanless power supplyFigure 24: +3.3 V rail during test five at 401.4 W (8.8 mV)

Let’s see if we can pull even more from the Seasonic X-400 Fanless.

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Author: Gabriel Torres

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.

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