We can’t understand how a manufacturer label a 450 W power supply as a 750 W and get away with it. We thought we had already got rid of this kind of thing here in the US, but we guess we were wrong.
Even if Coolmax CUL-750B could deliver its promised wattage it would still be a bad product, since its cables are short and it has only four SATA power connectors.
On the other hand, voltage regulation and noise/ripple levels are excellent, and efficiency stayed all the times above 80%. But please keep in mind that two samples from this unit burned when we pulled 500 W from it, so probably this unit would present efficiency below 80% if we were able to pull its labeled wattage.
If you take a closer look at our tests, you will see that this unit achieved its efficiency peak at 200 W. Efficiency is usually plotted as an inverse parabola, reaching its peak somewhere between 40% and 60% of its maximum wattage. Therefore, using the maximum efficiency we’ve seen in our tests, we could easily calculate that the maximum wattage for this power supply would be somewhere between 333 W and 500 W – matching with a fantastic precision what we found during our tests.
By the way: the manufacturer says the fan from this unit is 140 mm, but this is wrong, this unit uses a 135 mm fan.