I'm surprised at the number of people who replied without actually responding to his question or offering any options. Telling him 2x5770 on a 500w psu is "imminent failure" is laughable.
Haha, exactly, I'm running 2 hd 5850s and a hd 6850 on a 550w corsair atm. Undervolted them to reduce my PSU load a bit and it works great .
APEX is junk, period.
Either spend $100 on a PS, or say bye bye to the entire PC in a few days/weeks/months.
I had a Apex 500W, and it craps out when I pull 250w from it.