Efficiency is measured in terms of the relationship between the output and the input power, i.e., how much energy the power supply draws from the mains in order to supply the PC system with the required electricity. Our test produced differences of up to 15%. The best efficiency, at 78 percent, was achieved by the FSP400-60PFN. With output of 397 Watts, this power supply required an input power of 571 Watts. This means that 174 Watts must be dissipated as heat.

The devices from Verax, Enermax and Noisemagic all revealed good efficiency of around 75%. The Coba ATX-400W, with efficiency of only 64%, dissipates 207 Watts as heat. And at 65% efficiency, the Redux TSP-420P4 also falls below the average.

Quiet Operation

A power supply that produces lots of power unfortunately also generates a lot of heat; 200 Watts and up must be dissipated as heat. Despite actively regulated fans, our lab technicians measured up to 60°C inside the test candidates. For most power supply components, however, an operating temperature of 50°C is the absolute maximum to guarantee flawless operation and to prevent premature aging of parts.

Power supplies are equipped with fans to provide adequate cooling. As a rule, one or two fans are included in power supplies; PC Cooling and Redux integrate as many as three. In the test, however, these units did not have significantly lower temperatures than the devices with one or two fans.

As with CPU heat sinks, these fans produce an irritating noise that can make concentrating on your work at the PC difficult. To avoid loud noise levels during operation, all manufacturers have fitted their devices with automatic fan regulators. They ensure that fan speed is automatically adjusted to the temperature in the power supply. Low power-supply loads mean that the fan turns more slowly and is much quieter.

The quietest power supply in the test was the Seasonic at low load: with noise levels of 25.4 db(A), it is almost inaudible. At full load, on the other hand, the 45 dB(A) it produces are very audible and too noisy. The Zalman ZM400A-APF, in second place, has a noise level of around 27 db(A) at low load, and even at a full load runs at a quiet 37.7 dB(A).

Additionally, the manufacturers employ various methods to reduce noise levels. Verax, for example, has integrated a special radial fan it developed into the ST-400 HLP. The advantage of the Verax fan is its low noise levels. At full load, the Verax device was the quietest in the test at 34.1 dB(A).

Other power supplies, meanwhile, fail to impress with their high volumes - those in the 450 to 520 Watt class in particular: the very loud Herolchi HEC-450LR-AT produced over 50 db(A). At 60 dB(A), the Topower Top-520 MP was the loudest power supply in the test.