Contents
Rexpower PX-400
At only 118mm long, this is physically the smallest power supply in this round up. It is also the ugliest, with a grainy and unfinished look to the casing. Interestingly, this unit also has fewer screws than most, with only three to hold the casing together, and two for the fan.
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It sure gets a thumbs up from the manufacturer, but somehow, I think it will get a thumbs down from me. Like the Excel and Sun Pro, it’s a dated, 5V-heavy design.
Load Testing
Test 1 (117.33W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 4.92A | 12.29V | 44.0mV |
| 5V | 5.01A | 5.01V | 19.4mV |
| 3.3V | 9.82A | 3.24V | 4.0mV |
| −12V | 0A | −12.99V | 17.0mV |
| 5Vsb | 0A | 5.06V | 4.2mV |
| AC Power | 153.7W | ||
| Efficiency | 76.34% | ||
| Power Factor | 0.66 | ||
Test 2 (201.85W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 9.86A | 12.33V | 46.2mV |
| 5V | 9.90A | 4.95V | 18.8mV |
| 3.3V | 9.73A | 3.21V | 4.2mV |
| −12V | 0.11A | −12.91V | 48.8mV |
| 5Vsb | 1.0A | 5.02V | 6.0mV |
| AC Power | 266.5W | ||
| Efficiency | 75.74% | ||
| Power Factor | 0.64 | ||
Test 3 (260.02W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 14.66A | 12.22V | 71.2mV |
| 5V | 9.96A | 4.98V | 14.2mV |
| 3.3V | 9.73A | 3.21V | 4.0mV |
| −12V | 0.11A | −13.05V | 51.2mV |
| 5Vsb | 1.0A | 5.02V | 5.0mV |
| AC Power | 342.5W | ||
| Efficiency | 75.92% | ||
| Power Factor | 0.61 | ||
Test 4 (311.82W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 19.2A | 12.0V | 87.8mV |
| 5V | 10.02A | 5.01V | 14.6mV |
| 3.3V | 9.73A | 3.21V | 4.0mV |
| −12V | 0.11A | −13.24V | 56.8mV |
| 5Vsb | 1.0A | 5.02V | 5.2mV |
| AC Power | 431W | ||
| Efficiency | 72.35% | ||
| Power Factor | 0.61 | ||
And, that would indeed be a thumbs down. Sure, I’ve seen worse from the Sun Pro, but I’ve also seen better from the Thermal Master. The voltage regulation was generally OK, but the −12V rail was always quite on the low side, starting at -12.91V and during test 4, it was below the minimum −13.2V allowed in ATX specifications. The ripple suppression was also average. Yes, it was acceptable, but it was unspectacular on the 12V rail. The 3.3V rail, on the other hand, was excellent, maxing out at only 4.2mV. Maybe this PSU uses linear regulation for the 3.3V rail. The efficiency was another let-down, peaking at just over 76%. I couldn’t pull much more than 310W from it. When I asked for more, it lasted about 30 seconds before there was a soft pop and it died.
| Rail | Test 3 (256.79W) | Test 4 (305.53W) |
| 12V |  |
 |
| 5V |  |
 |
| 3.3V |  |
 |
| −12V |  |
 |
| 5Vsb |  |
 |
A Look Inside
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The PX400’s input filtering consists of a common-mode choke, two polyester film caps, and three ceramic caps. There should be an extra choke in there, and the capacitors are not safety rated. Two Fairchild KSE13009s, rated at 12A each, are used as the switching transistors, one of which was visibly cracked. Similar parts have been able to deliver more than just 310W in other power supplies, so there was probably something else which caused them to fail. The two capacitors are 560μF parts branded Metacon, a brand I’ve never heard of before, and the bridge rectifier is a 4A part.
Moving on to the secondary side, The 12V rail’s rectifier is a Taiwan Semiconductors FR1003G fast recovery rectifier rated for just 10A, although I was able to pull a fair bit more than this without damaging it. The most likely explanation is that the fan is wired straight to the 12V, so it keeps the rectifier cool enough to allow for more current. The 5V rail uses a General Semiconductors SBL3040PT Schottky rectifier rated at 30A. Like the Sun Pro ATX-550W, the PX-400 uses linear regulation from the 5V rail to power the 3.3V. The transistor used is a Niko Semiconductor P45N03LTG, rated at 60A at 25°C and 38A at 100°C. The capacitors used on the secondary side are made by CS and Fuhjyyu, neither of which are known for making reliable parts.
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The fan and transformers are made by Ever-Power, which pretty much gives the OEM away – Key Mouse Electronics, which is also known as K-Mex. They are about the only ones who use Ever Power parts in their power supplies. As I mentioned earlier, the fan is wired directly to the 12V output, and it was fairly noisy. It was beginning to fail as well, making a loud ‘growl’ for the first five minutes after being powered on.
Specifications and Conclusions
| Real Wattage | 310W |
| OEM | Key Mouse Electronics (K-Mex) |
| PFC | None |
| Price | Unknown |
| ATX Connector type | 20 pin |
| Worst-case voltage regulation (12v, 5v, 3.3v) | 2.8%, 1.0%, 3.6% |
| Worst-case ripple (12v, 5v, 3.3v) | 87.8mV, 19.4mV, 4.2mV |
| Worst-case efficiency | 72.35% |
| Input filtering | Inadequate – and not safety rated |
| CPU Connector | ATX12v (4 pin) |
| PCIe Connectors | None |
| Molex (Peripheral) Connectors | 4 |
| FDD Power connectors | 2 |
| SATA Power connectors | None |
Pros: At least nothing was out of spec
Cons: Can’t deliver 400W, Noisy, Not enough connectors, Inefficient, Ugly, Low quality fan and capacitors, Input filter needs another coil, Average voltage regulation, Average 12V ripple suppression.
Score: 2/10
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