Bro eyern..

I guess ur PSU is not sufficient enough for ur GC's.. u got a zotac AMP there.. it is same as a OC version of other brand.. (OC version need more juice of power)

Try google for a sufficient PSU to power dual zotac AMP since u got that one..

Before i go for sli, i'm using CM550W Real Power... that is for normal setup.. but for OC (proc,rams,GC's) u need at least 600Wtt of real power PSU...more is better..

if u hav an extra bajet, just get the 1k watt psu. Can power dual gtx280 in future.  Hehe:)
If u dont, get 750watt from CM.
600w is just ngam2 la bro.

For ur earlier post, yes i would say ur psu is too low for ur setup, it'll stress ur psu too much, heat-up etc, and in ur case its not enough juice.   Get true power >550 at least, 600> best, ive used CM Real Power 550 for my Sli with 2 oc-ed 88gt's n oced proc, runs fine . . . though its a bit too much for the psu coz of ocing.   Now im using CM 850 for my gtx260+ . . . single though, not sure if its sufficient for Sli.