i got GTX460 (see sig) from asus and they recommend power supply with at least 24A on the 12v rail. so i think it is safe to use PSU with 24A on the 12v rail with GTX560 (i assume the OP have non Ti GTX560 since he does not mention the Ti moniker ). having said that he still needs decent PSU to run GTX560. most decent 450-550w PSU that i know should at least have 30A on the 12v rail.
I stand corrected ! If i would have seen your gpu earlier i wouldn't have made that statement probably. I allready did think it was recommended for overclocking.
Butttttt, if he ever wants to oc . . .it better be a good brand psu then to handle that.