Corsair’s Mike Clements has published a detailed article about how to select the ideal PSU (Power Supply Unit). With modern CPUs and especially modern GPUs (GTX 480 or the brand new HD 6870), selecting the good PSU is important because even if the PSU seems to support the load, under some situation you can experiment an unexpected and brutal shutdown caused by the PSU. This is the case with graphics cards like high end GTX 400 or with multi-GPU systems (CrossFire and SLI).
PSU Selection in Four Simple Steps
The four steps for selecting a PSU are very simple. The first step is to estimate the power needs of your CPU and motherboard. Next, determine how much power your graphics solution will require. Then, factor in additional components, and overclocking impact. Finally, determine what wattage PSU you will need by totaling these power requirements and factoring in some efficiency considerations.
And the most important:
We recommend that you select a PSU that will meet your system’s target power requirements when running at 80% of its rated wattage. Why? The reason is that PSUs are most efficient in this range, and therefore will have quieter fan operation.
Example: if the total power you need is 625 watts, this means the “sweet spot” would be a PSU with wattage of (625/0.80) = about 781W.
For determining the power consumption of your graphics card, use the GPU TDP database 😉