I have a question related to the PSU required by nvidia gtx 260. Reading multiple websites shows that the gtx 260 uses 270 W. Calculating the amps required 270/12 = 22.5 A. If the card only uses 22.5 A when under load why does it say on the manual that it needs a psu with 36 A on the +12 ? 1 HDD usually uses 1A.

If I am correct, a good psu with 38A on the 12V should be plenty for 2 HDD, 1 DVDRW and a gtx 260, right?

The card uses nowhere near that amount of power on it's own, look around for posts by invisik , he's running 2 of them in SLI and an oc'ed Quad on a 34 amp psu.

the gtx 260 uses i believe around 182w at peak. u would be fine using a good quality 400-450w psu with about 27-30amp to be safe. im pushing my psu to its limit so if u do sli gtx 260 later on i would recommend a really good psu 550-600w with about 36-40amp.
(btw ppl telling u need like 800-1000w r just simply retards)

http://www.xbitlabs.com/articles/v [...] html#sect0

I have a case with a built in unbranded 600 watt psu which i was told was probably not powerful enough for even an 8800gt, the reason being just because it was a relatively high wattage the rails may not have the necessary current and it could damage my pc. In this case would it not be powerful enough for a 260? ALso if I were to try it could it serioulsy damage my pc?

depends how many amps u have on the rails.
i believe there is a slight chance it can damage it but i would try it, usually it just shuts down if the psu cant run it.