If you are looking for an efficient power supply with moderate wattage (within 600 W), then there are two choices among the tested models: Seasonic X-560 (SS-560KM) and Cooler Master Silent Pro Gold 600W, we haven’t tested any other PSUs with similar characteristics yet. The Seasonic is better in acoustic comfort, efficiency and output voltage ripple but the Cooler Master is cheaper while being not very inferior to its opponent in electrical parameters.
As for the other products we’ve just reviewed, the PSUs from Cougar and OCZ are comparable in price, the OCZ being slightly more expensive, but offer different sets of advantages. The OCZ ZX 1000W is better electrically (cross-load stability, efficiency, voltage ripple) than the Cougar GX series but the latter are quieter at medium and high loads, have better compatibility with UPSes and feature an eye-catching exterior.
The 850-watt Gold-certified model from Seasonic stands out among the rest. It is considerably more expensive than the other products reviewed here, although its wattage is lower than that of the Cougar and OCZ products. This implies superior characteristics, yet we don’t find them in practice. The Seasonic SS-850KM is let down by its not-very-stable +12V voltage as well as by the unjustifiably aggressive behavior of its cooling fan at high loads. Although these downsides are not critical, you may want to think twice before paying extra for this PSU. When you pay more, you want to have nothing but advantages for your money, yet the Seasonic SS-850KM can only offer you a different combination of highs and lows in comparison with the other products.