If you're planning on using two graphics cards in your desktop PC, and perhaps even try your hand at overclocking those along with your processor, it's advisable to get a PSU of between 750 and 950 watts. There are a huge number of these on the market, so it's difficult to know which one is best for your needs. Hardware.Info tested 28 power supplies in this category, to separate the wheat from the chaff. See all components buying advice.
Earlier this year Hardware.Info tested 43 power supplies between 500 and 700 watts. This type of capacity is plenty for the majority of PCs, especially if you'll only be using a single graphics card. Once you begin using two video cards and start to overclock, you will quickly run into the limitations of a 700-watt or lower PSU.
Most current processors have a TDP of about 95 watts. TDP stands for thermal design point, which basically is the maximum power usage. High-end graphics cards have a TDP of around 250 watts. So when you combine two video cards, add the CPU, add 100 watts for all the other PC components, you're already at 700 watts. Power supplies are the most efficient when they run at half capacity. When you overclock, even with just air cooling, the power usage of GPUs and CPUs can increase by another 30 to 50 percent, and even more for good overclocking processors. These are all very good reasons for getting a PSU with enough capacity.
Eight out of the 28 tested PSUs have a maximum capacity of 750 watts. Three are 800-watt models, and one is 900 watts. The 16 others have a capacity of 850 watts. Seasonic stands out with its 760- and 860-watt labeling, which was probably an idea from their marketing department.
It's striking that all but four of the PSUs are single rail models, which means they have a single circuit for the 12V current. Single-rail power supplies have a number of advantages. It's easier to make them energy-efficient, which is probably a big reason for their popularity. They can also channel their entire output for 12V components via one or more cables, which is great for overclockers, who for example want as much power as possible for the 8-pin CPU connector.
The advantage of multi-rail power supplies is that, if one component causes interference, it will have little to no effect on the components connected to the other cables. The Antec HCG-900, Antec HCP-750 and Enermax Revolution 87+ 850W are multi-rail PSUs, with four rails each. The Be Quiet Dark Power Pro 10 850W is also multi-rail, but it has an OC-Key button that turns it into a single-rail PSU.
Almost every power supply is modular in this test, so you only usethe cables you actually need. It keeps your chassis free of clutter, improving the airflow and thereby also the cooling. Five of the PSUs aren't modular, the Thermaltake Toughpower 750W, the Cooler Master GX V2 750W, the Antec HCG-900, the Corsair G800 v2 and the Fractal Design Tesla R2 800W.
The number of connectors varies quite a bit. The Be Quiet Dark Power Pro 10 850W is the only one with seven PEG connectors. Six connectors are found on the Corsair HX850, Cooler Master Silent Pro M2 850W, the High Power Direct 12 850W, the Cooler Master Silent Pro Hybrig 850W, the Enermax Revolution 87+ 850W and the NZXT Hale 850. The rest come with four connectors. Four is enough for two high-end graphics cards, but we prefer having a little more flexibility. The number of SATA connectors also varies, from six on the entry-level PSUs to 12 on the deluxe ones. The number of molex connectors stretches from 12 all the way down to two. The exact number for each PSU can be found in the chart.
For cable management it's important that cables are long enough. Particularly PEG cables are frequently too short for this. Cooler Master has the longest PEG cables on the Silent Pro Hybrid and Silent Pro M2, they're 75 cm. On the Enermax Revolution87+ and the OCZ Fatility, the PEG are shorter than 50 cm, which is barely long enough for cable management.
The rest of this review you can read on Hardware.Info.