Hmm... I don't like how it's got three +12v rails but I don't see why that would have an impact on it powering a 480.
Not sure how that PSU is setup but if you can, make the 480 the only item on, say, rail 3. So it'd have access to the full 19A if it need. As per nVidia
it only needs 600w so I'd imagine you should be good. Cutting close imo, but it should work none the less.