Can you use anything from your PSU to power video cards that require several power sources? Like, anything from your PSU that will literally fit into the card? After a couple of swaps and upgrades, I've run into where I need an adapter and a work-around with the plugs to power the second video card. Everything fits correctly, but I'm afraid to fire it up without some expert knowledge.
Firstly, can you say what you want to power and what PSU you have? The way i read it it just sounds like you need the right PSU, mine can power two cards but it has all the correct cabling. I imagine this is a different scenario though so specifics will help people help.
I've done it before. I was testing two 3870X2 with an 8800 ultra for Physx and only had an 800w psu. I used a separate 450w for the 8800 and if worked fine. Just make sure you switch on the GPU first as the board will spaz if it thinks the pcie power connectors are not connected. Edit, seems I'm confused. It depends on the PSU. Is it single rail or multi? If it's single rail all of the 12v and grounds go back to the same place so yes, it would be fine. If it's multi rail and you overload one then you'll be in trouble. I would do some research on your PSU. Find out what type it is. If it's multi rail and good (like my Platimax) it will tell you where the rails are etc. If it's junk it won't.
outside of the pinout being different, which one can get an adapter for, realistly the wires are going to the exact same points in the power supply edit: does anyone make "multi rail" supplies anymore, thought we got over that marketing BS
