Corsair CX400W Power Supply

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TEST RESULTS

The ambient temperature was 21~23°, and the ambient noise level was 11 dBA. Note that our testing platform utilizes separate loading apparatuses for 12V1 and 12V2, and data is collected accordingly, but in the CX400W 12V1 and 12V2 are the same line, and they are treated accordingly in all data analyses. There is no downside to our method.

OUTPUT, REGULATION & EFFICIENCY: Corsair CX400W
DC Output Voltage (V) + Current (A)
DC Output
AC Input
Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.38
0.98
12.38
0
5.1
0.98
3.38
0.97
0.1
0.1
22.1
35
63.2%
12.35
0.98
12.35
1.71
5.11
0.98
3.38
0.97
0.1
0.1
43.2
59
73.2%
12.35
1.93
12.35
1.73
5.1
1.94
3.38
1.85
0.1
0.4
64.5
83
77.8%
12.35
1.92
12.35
3.43
5.1
1.95
3.38
2.74
0.2
0.5
90.2
111
81.2%
12.34
3.82
12.34
4.93
5.09
4.53
3.38
2.66
0.3
1
148.6
181
82.1%
12.3
5.67
12.3
6.54
5.08
5.4
3.38
5.27
0.4
1
205.2
244
84.1%
12.27
7.67
12.27
7.91
5.08
5.5
3.39
5.32
0.5
1.5
250.6
293
85.5%
12.26
8.63
12.26
9.43
5.07
7.89
3.39
7.82
0.6
1.8
304.1
364
83.6%
12.25
11.34
12.25
9.52
5.07
9.42
3.39
8.66
0.7
2.1
351.6
427
82.3%
12.2
13.04
12.2
11.01
5.05
10.93
3.39
10.1
0.7
2.1
401.7
493
81.5%
Crossload Test
11.88
13.52
11.88
14.94
5.22
1
3.38
0.95
0.1
0.1
348.2
420
82.9%
+12V Ripple (peak-to-peak): <16mV @ <400W
+5V Ripple (peak-to-peak): <4.4mV @ <400W
+3.3V Ripple (peak-to-peak): <5.6mV @ <400W
NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings. It is a tiny portion of the total, and errors arising from inaccuracies on these lines is <1W.

OTHER DATA SUMMARY: Corsair CX400W
DC Load (W)
22
43
64
90
148
205
250
304
351
401
Intake °C
21
21
24
25
30
30
29
30
31
36
Exhaust °C
24
25
29
31
35
37
38
40
45
51
Temp Rise °C
3.0
4.0
5.0
6.0
5.0
7.0
9.0
10.0
14.0
15.0
Fan Voltage
4.2
4.2
4.2
4.2
6.2
10.2
11.2
11.2
11.3
11.3
SPL (dBA@1m)
19
19
19
19
26
32
35
35
35
35
Power Factor
0.86
0.96
0.98
0.997
1
.99
1
1
1
1
AC Power in Standby: 0.7W / 0.087 PF
AC Power with No Load, PSU power On: 9W / 0.68 PF
NOTE: The ambient room temperature during testing can vary a few degrees from review to review. Please take this into account when comparing our PSU test data.


1. EFFICIENCY This is a measure of AC-to-DC conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency or better at all output power loads. 80% efficiency means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost as heat within the PSU. Higher efficiency is preferred for reduced energy consumption and cooler operation. It allows reduced cooling airflow, which translates to lower noise. The 80 Plus standard also requires 80% efficiency at 20% of rated load or higher.

At a minimal and unrealistic 20W load, efficiency was poor at 63.2%. By 65W, which is a nominal idle load for most systems these days, efficiency rose to about 78%. Better than 80% efficiency was seen at all loads over 90W up to the maximum rated load, and a 85.5% peak was reached at 250W. As we've seen in many other power supplies, efficiency began to drop as maximum rated power output was reached, likely due to the rising temperatures at those loads.

These are good results, although 80%+ efficiency is reached a little beyond the 80W load that represents 20% of maximum load. Note that the 80 Plus testing is done at typical room temperature (18~28°C) while our test conditions feed the heat of the PSU output back into its operating ambient, which makes for a much hotter, more demanding high power load test. In spite of this, the CX400W efficiency remained above 80% even to full load.

2. VOLTAGE REGULATION refers to how stable the output voltages are under various load conditions. The ATX12V Power Supply Design Guide calls for the +12, +5V and +3.3V lines to be maintained within ±5%.

The CX400W performed magnificently, with maximum overshoot and undershoot seen at no load and crossload conditions, respectively. The worst on the 12V line was an overshoot of 3.17% at no load, and crossload conditions only managed to drop the voltage 1%. The 5V line, similarly, was 2.2% over at no load, but reached around 4.4% over during the crossload test, still within spec. Both lines tended to get closer to their target voltage as the load increased, decreasing percentage overshoot. The 3.3V line acted contrarily, increasing overshoot as the load increased, reaching a maximum of 2.72% at maximum load, and generally unaffected by the crossload test.

3. AC RIPPLE refers to unwanted "noise" artifacts in the DC output of a switching power supply. It's usually very high in frequency (in the order of 100s of kHz). The peak-to-peak value is measured. The ATX12V Power Supply Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was ridiculously good at all power levels, staying under 16mV on the 12V line over the entire range, and under 4.4mV and 5.6mV on the 5V and 3.3V lines, respectively. Close to the best ripple we've measured in the past, and fantastic at the price.

4. POWER FACTOR is ideal when it measures 1.0. In the most practical sense, PF is a measure of how "difficult" it is for the electric utility to deliver the AC power into your power supply. High PF reduces the AC current draw, which reduces stress on the electric wiring in your home (and elsewhere up the line). It also means you can do with a smaller, cheaper UPS backup; they are priced according to their VA (volt-ampere) rating. Power factor was good for this PSU, running no lower than 0.96 for every point above 50W, though a PF of 0.86 was measured for 20W. At this low power, however, the difference the power factor makes is not nearly as significant as at, say, 400W.

5. LOW LOAD TESTING revealed no problems starting at very low loads. Our sample had no issue starting up with no load, either, and the power draw was modest.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W load with 120VAC through the hefty variac in the lab. The variac was then dialed 10V lower every 5 minutes. This is to check the stability of the PSU under brownout conditions when the AC line voltage drops from the 120V norm. Given the difference between the web specifications and the specifications written on our power supply, we tested down to 90V.

Most full-range input power supplies achieve higher efficiency with higher AC input voltage. SPCR's lab is equipped with a 240VAC line, which was used to check power supply efficiency for the benefit of those who live in 240VAC mains regions.

Various VAC Inputs: CX400W @ 300W Output
VAC
AC Power
Efficiency
240V
347W
87.6%
120V
360W
84.4%
110V
363W
83.7%
100V
365W
83.3%
90V
368W
82.6%

Efficiency improved around 3.2% with 240VAC input at this load. The power supply also performed appreciably all the way down to 90V as promised, still staying above 80% efficiency. Neither voltage regulation nor ripple changed appreciably during the test.

7. TEMPERATURE & COOLING

The CX400W stayed reasonably cool throughout the test, demonstrating a double digit temperature rise around 300W, and staying at a stable 15ºC rise at maximum load. This is quite impressive for the price point, but the tradeoff is higher fan speed, as explained below.



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