If it's one of the models listed in tier 1, 2 or 3, it's not bad:http://www.tomswiki.com/page/Tiered+PSU+Listings?t=anon
Look at the sticker on the side of the psu. If it has a combined 26A on +12v rails or more, it is ok:http://www.evga.com/products/moreinfo.asp?pn=640-P2-N827-AR
Or you can tell me the max wattage on the +12v.
The actual power consumption isn't as high as the psu manufacturers make it out to be. The 480w can overclock. You can try a mild o/c & se e if there are any stability issues like instant reboots/shutdowns.