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Zumax ZU400W
Zumax is a budget division of Topower – a company which I haven’t seen much of over the last few years. The last Topower unit I got my hands on was the Global Win SAF450 – an old but reasonably well performing unit. Let’s see if this power supply is at least as good as it was.
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Again, we have a label which incorrectly claims two 12V rails. This power supply really only has one. Like most other power supplies around the $20 mark, it is plain grey in colour.
Load Testing
Test 1 (116.05W Load)
| Rail | Load | Voltage | Ripple |
| 12V | 4.6A | 12.29V | 41.8mV |
| 5V | 5.03A | 5.03V | 19.2mV |
| 3.3V | 10.18A | 3.36V | 27.0mV |
| −12V | 0A | −12.32V | 26.2mV |
| 5Vsb | 0A | 5.05V | 32.2mV |
| AC Power | 151.1W | ||
| Efficiency | 76.80% | ||
| Power Factor | 0.57 | ||
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Test 2 (199.09W Load)
| Rail | Load | Voltage | Ripple |
| 12V | 9.2A | 12.19V | 68.2mV |
| 5V | 9.78A | 4.89V | 31.6mV |
| 3.3V | 10.0A | 3.30V | 28.4mV |
| −12V | 0.11A | −12.66V | 61.8mV |
| 5Vsb | 0.98A | 4.89V | 42.4mV |
| AC Power | 265.0W | ||
| Efficiency | 75.13% | ||
| Power Factor | 0.55 | ||
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Test 3 (251.2W Load)
| Rail | Load | Voltage | Ripple |
| 12V | 13.6A | 12.02V | 86.0mV |
| 5V | 9.88A | 4.94V | 38.8mV |
| 3.3V | 9.97A | 3.29V | 28.8mV |
| −12V | 0.11A | −12.95V | 78.0mV |
| 5Vsb | 0.97A | 4.86V | 47.4mV |
| AC Power | 341.1 | ||
| Efficiency | 73.64% | ||
| Power Factor | 0.56 | ||
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Test 4 (298.95W Load)
| Rail | Load | Voltage | Ripple |
| 12V | 17.8A | 11.86V | 108.8mV |
| 5V | 9.94A | 4.97V | 47.4mV |
| 3.3V | 9.94A | 3.28V | 29.8mV |
| −12V | 0.11A | −13.43V | 104.2mV |
| 5Vsb | 0.97A | 4.83V | 50.4mV |
| AC Power | 420.2W | ||
| Efficiency | 71.22% | ||
| Power Factor | 0.54 | ||
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The 12V rail started at 12.29 and finished at 11.86V, which gives us 0.29V (2.42%) Regulation and a 0.43V (3.58%) drop. On the 5V, we saw between 5.03V and 4.89V, which equates to 0.11V or 2.2% regulation and 0.14V (2.8%) variation. The 3.3V rail was at 3.36V during Test 1 and 3.28V during Test 4, giving us 0.06V (1.82%) regulation and a 0.08V (2.42%) drop. This is not a great result on any of the rails.
The efficiency was woeful. 76.8% was as good as it got, and during Test 4, it was down to just 71.22%. 300W was also as much as I was able to squeeze from this power supply. When I asked for 350W, it blew both switching transistors.
| Rail | Test 3 (251.2W) | Test 4 (298.95W) |
| 12V |  |
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| 5V |  |
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| 3.3V |  |
 |
| −12V |  |
 |
| 5Vsb |  |
 |
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The ripple suppression was only borderline passable. By Test 4, it was very close to the maximum allowable limit in the 12V and 5V rail, and was slightly above on the 5vsb rail (not that your hardware will notice the 0.4mV difference). If the ripple suppression is borderline now, it won’t take long before the capacitors wear enough to let the ripple get out of spec.
Disassembly
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The Zumax’s nput filtering consists of nothing but three Y-Capacitors (including the one after the rectifier), which is nowhere near enough components. The other key components are a 4A bridge rectifier, 470µF Sun branded primary capacitors, and rather ‘well done’ 8A MJE13007 switching transistors – which are completely incapable of sustaining a 400W Load.
The 12V rail uses an F20C20CT rectifier – a Fast Recovery Rectifier rated for 20A. It would be better to use a Schottky rectifier instead, as they offer better efficiency. I couldn’t identify it’s manufacturer, but in all likelihood, its specifications are identical to those of the MOSPEC F20C20C. The other two rails use a MBR2045CT rectifiers, which are also rated at 20A, although they are the more efficient Schottky rectifiers. Again, I couldn’t identify their real manufacturer, but the specs are, in all likelihood, the same as the ON Semiconductors MBR2045CT. The capacitors on the secondary side are all from Asia’X, which are actually made by the dreaded Fuhjyyu – some of the most unreliable capacitors on the planet.
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The fans are both branded Zumax. The 92mm fan is actually made by EverCool, and, while I can’t confirm this, I suspect that the 80mm fan is too. They are temperature controlled, but they were not quiet. I could hear them during test 1, and they were getting very loud during Test 2. It wasn’t quite as loud as the Aozhong, but still loud enough to get annoying. The 80mm fan did not have sufficient lubricant in the bearing – just a small amount of thick grease. The 92mm fan didn’t have a removable plug on the bearing, so I couldn’t check its lubricant. I wouldn’t be surprised if it’s just as insufficient, however. The heat sinks have a decent amount of surface to air contact, but are too thin to effectively conduct heat away from the silicon components.
Specifications and Conclusions
| Real Wattage | 300W |
| OEM | Topower |
| PFC | None |
| Price | $20 (USD) |
| ATX Connector type | 20+4 pin |
| Worst-case voltage regulation (12v, 5v, 3.3v) | 2.4%, 2.2%, 1.8% |
| Worst-case ripple (12v, 5v, 3.3v) | 108.8mV, 47.4mV, 29.8mV |
| Worst-case efficiency | 71.22% |
| Input filtering | Inadequate |
| CPU Connector | ATX12V (4 pin) |
| PCIe Connectors | None |
| Molex (Peripheral) Connectors | 4 |
| FDD Power connectors | 1 |
| SATA Power connectors | 2 |
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Pros: None
Cons: Can’t deliver labelled rating (−2), Low quality capacitors (−3), Mediocre ripple suppression (−1), (Mediocre Voltage Regulation (−1), Low quality Fans (−1), Very inefficient (−1), Loud (−1)
Score: 0/10
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