Hi there!

I'm building a mining rig (wheter it's profitable or not), my specs are:

Z77A-GD55 (Mainboard), Core i3-2100 (CPU), Corsair Vengeance 8GB (RAM), 500GB Sata (HDD), and now the problem:

I have a generic "500 Watts" (PSU), with this one, I'm pretending to supply the mainboard and HDD.

So far, the CPU works, it turns on and everything is working as expected.

The problem is... that 1st PSU won't be able to supply the 3 GPU I have (PowerColor R9 280x, Sapphire 7970, Gigabyte 7970).

So, AFAIK, I can supply those GPU with a different PSU in the 12V PCI connectors. So I buy this PSU ---> HP DPS-1200FB.

I asked before about turning on the GPU's PSU and then the mainboard PSU and there's no problem. In fact I can use a little relay to turn them both at the same time.

So yes, so far everything is OK.

But now another problem appears.

I'm using 3 of this usb risers, and now I'm not 100% sure of how should I supply them.

Some people says I must supply the usb risers with the 5v and 12v and both grounds (I mean 1 molex) from the mainboard PSU, and then only use the HP Server PSU to supply the PCI-6 and PCI-8 ports of the GPUs.

Some other people says I must get 5v and one ground from the generic PSU and 12v and the second ground from the HP PSU... to supply the mentioned risers.

I don't really know what to do, I'm afraid of damaging my GPU's. Is there anybody with experience here that can help me out?

Thanks in advance.