Ok so I am running a Thermaltake 500 watt power supply with 2 12V rails 1 at 15A and the other at 14A. I think my 7800GT is being underpowered. The rail fluctuates from 11.84V to 11.72 V idle and load respectively. I run an athlon 64 3500+ with 2 GB DDR ram 1 HD, DVD drive, DVD-RW drive and 4 fans. Am I maxing it out? Can I get by with it? (I also have a 430 watt thermaltake power supply with an 18A 12V but only one though)

Please help with suggestions or confirmation or anything!

I think all Tt PSUs apart from the Toughpower series do this... I have a Purepower 480 and while it is about 8 years old, and reliable, it does have the same voltage droop... I replaced the capacitors in the end which helped a bit...

11.76 is only 2% less than 12v though, nothing to really be too concerned about, as long as it is stable, it's ok

in addition apparently eVGA recommends a minimum of 18A to power this sucker. Will it draw any from the board and can i get by? In addition, hardnrg please explain about what you are talking about with replacing the capacitors!

Replacing the capacitors requires some soldering experience, so if you don't know what soldering is, I would not recommend you to try it out on a PSU

18A on a single rail, but if you have dual rails, it's fine. I ran a 7800GT off of an Aspire 520W PSU once, which had dual 12V rails at 13A each I think... that was a crappy PSU

That 18A is for the whole system though. There's no way a 7800GT needs 18A on its own. That's about 216W of power. My whole system (with a 7800GT) at full load barely consumes 250W, and that's heavily overclocked.

If you're not noticing any problems with performance, I wouldn't worry too much.

Thanks! it seems to blue screen on startup but I cannot read it (it has issues starting up regardless of graphics card, but i never get the blue screen)

I'd be willing to bet that a blue screen at load is NOT a power problem. Generally, if you're having problems with not enough power to the video card, it'll happen when you're gaming, or whenever the video card is really exerting itself. That's not really the case at boot up.

You might try reinstalling drivers to fix that blue screen on boot. Without knowing more of the history, it's hard to say what it is.