Some manufacturers leave speed adjustments (and thus, noise levels) in users' hands. Besides automatic fan regulation, the Enermax EG465AX-VE(W) FMAX also offers manual speed adjustment for the fan at the rear. The speed can be set anywhere between 1200 and 2500 RPM by using the potentiometer on the reverse of the power supply. To prevent damage to the power supply, this fan also has automatic fan adjustment: if the setting selected by the user is too low for the power supply's output, the fan speed is automatically accelerated to avoid overheating.

The power supplies from PC Cooling and Redux employ a three-phase solution. These two brands offer a choice between a low and high fan speed, plus automatic fan adjustment. The PC Cooling Ultra-Silent 400 proved that this solution can also be counterproductive. When set to "low," the power supply is louder than if the "auto" setting is selected. This is partly because the manufacturer sets a fixed basic speed in order to ensure adequate cooling at higher loads, as well. Although the power supply is sometimes noisier, this method does prevent damage from occurring to the device through overheating.

Cable Overload

In selecting a power supply, the focus should be on high output and low noise levels. It is equally important to consider the features it offers. Features to look for are the number of plugs for 5-¼" and 3-½" devices, as well as the number of connectors and cable length. Watch out, too, for the number and positioning of the hard drive and floppy drive connectors on the cable harness. At higher outputs, it is important to distribute the load across several cable connections. Two cable groups for up to ten drives are too few for a 520-Watt power supply, such as the Topower TOP-520 MP. The devices' supply voltage is too high for the connections. The Fortron Source device, on the other hand, offers only six hard-drive connections, but spreads them across five cable groups.

The number of connectors should also be taken into account. Six hard-drive connections can be considered an absolute minimum. No power supply in this test had fewer connectors. A system with two hard disks, a CD burner and a DVD drive would use all of these available connectors. Eight hard- and two floppy-drive connectors, such as on the Enermax and Seasonic power supplies, are the standard. A power supply that provides extra connections scores another plus. For example, Zalman's distributor can handle four case fans and be connected to a hard-drive connector.