There are some PSU calculators online, but they're very rough. Another thing to look at is how many amps there are on each rail. Beware though, you cannot just add the amps of multiple 12v rails together.
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Silent Tuned | 3D Marks 06: 11566
Q6600 2.4ghz CPU | Gigabyte GA-P35 LGA 775 MB
EVGA 8800gt 512mb Video Card
G.Skill 4GB Ram | Western Digital 400GB HD
X-Fi Xtrememusic Sound Card
Antec P180B Case | Scythe Ninja HSF
CM Real Power Pro 650watt PSU
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