Just wondering if my 500watt power supply would be enough to run a second 5770?

Dont go by what i say but i would get something more in the region of at least 550-600.I used to use a 550 with two 7900gs a few years back and then upgraded to an 850w coolermaster , cheap and quiet too.


check here 5770 ati psu recommendation

450 Watt or greater power supply with one 75W 6-pin PCI Express® power connector recommended

600 Watt and two 75 watt 6-pin connectors for ATI CrossFireX™ technology in dual mode

The information that came with my HD5870 cards said 650W for two cards. With both cards 100 percent and the 6 core CPU 100 percent, I measured the actual power draw at over 500W. I have well made PSU rated at 650W at 50C case temperature.

So, 500W in a real good PSU might just do it -- as an HD5770 uses significantly less power than an HD5870. Normally, one would not want to run a PSU at full rating. However, you might be running at 400 to 450 with two HD5770.

A "second tier" PSU might literally burn if used too close to its rating. Maybe you can find out the PSU recommendation at the AMD site or if you still have the "instructions" that came with the HD5770 card. Also, if you can find your PSU on Newegg (or find the instructions), then maybe you can find what the rated operating temperature is at 500W -- you want 40C or higher.

Don't take a chance. For $100 vs losing a major component(s) it isn't worth it. It is also a question of how much power is going to the 12v rail in a power supply. Wattage amount isn't always safe.

Trust this:
http://sites.amd.com/us/game/products/certified/Pages/certified-power-supplies.aspx

If you have multiple HDDs, you'll need to increase the wattage.

Copied from AMD site regarding HD5770:



So, they say 600W. They have a link to certified PSUs.

AMD HD5770 Requirements Page

P.S. I notice the on-line HD5870 page indicates 600W just like the HD5770. But, the instructions in the box for my cards said 650W. And, my system actually draws just over 500W at 100 percent (noted above). Shows that the "true absolute minimum" PSU is open to interpretation. Still, 500W would be a marginal "true absolute minimum" for HD5770 (might work, might not -- depending on CPU load and other things in the case). FWIW, A 650W PSU like mine below is $73 today (after shipping and rebate).