I am trying to build within a certain budget. I will be drawing power from 2 PSU. I am looking at 850w gold. 1 psu will power the system, 2 boards, and all risers where as the other unit will power the remaning 6 psu alone. I had an issue splitting riser to two PSU which gave a reverse current and blew one of them.
Either that or i get 1 PSU to power up the System and Risers and another PSU to power up the GPU. Rough calculations of 90watts per GPU alone would be sufficient. Ultimately this would be a better setup for me. But surely its going to be very messy....
You should not use a different PSU for the riser than you use for the GPU. The powered USB-cable risers should never have power beyond that necessary to carry the signal, and will not short something out (outside of a catastrophic failure). The GPU will draw some power from the riser, and some from the 6/8-pin on the card. These two sources should be the same.