Buying Power Supplies
Agent001 went shopping for power supplies but he made the same mistakes everybody else does i.e. judging a PSU by only its total power rating. He failed to check the most important specification on the PSUs namely the maximum current rating of the +12V rail(s). Since the +12V rail is the most demanding in a PC, its recommended that you buy a PSU that delivers the maximum power on its 12V rail. A 400W SMPS with a max current rating of, say 30A, on its 12V rail is better than a 450W SMPS that can deliver only say 25A on its 12V rail. If a PSU can deliver higher current on its 12V rail, it means that you can add more components on your PC without having to fear of running out of power. Even cooling fans draws power from the 12V rail. Almost 90% of the power required by a PC is drawn from its 12V rail. A higher current rating on the +3.3V and +5 volt rails is not necessary and can only lead to incorrect buying decisions. For eg, my 500W SMPS has the following ratings:
+3.3V -- 22A
+5V --- 16A
+12V1 --- 15A
+12V2 --- 16A
So the max power power on the 3.3V and 5V combined is approx 150W (3.3x22+5x16) and that of the 12V rail is about 370W (12x31). Which means that even though I have a 500W SMPS the effective power rating is just a little over 400W (considering that 370W accounts for 90% of the power).
For a good guide on PSUs have a look at these links
*www.silentpcreview.com/article28-page3.html
*www.silentpcreview.com/article265-page1.html
*www.hardcoreware.net/reviews/review-338-1.htm