Even when it was new that power supply was under-powered. It only had 30A(360w) on the 12v rail when it was new, and the caps being 3 years old probably means you are now closer to 20A(240w). I've seen 430w power supplies with stronger 12v rails than that PSU.
A good PSU is a must for any system, but it is extra important for a dual-card setup. A new PSU is where I would start. You don't have to go all out and get a 850w unit, but a CX600 would server you well and they aren't all the expensive.