I asked this in another thread.
I was told that as long as you don't plug two separate PSUs into one board you are fine. Here is what I am going to do for two of mine.
I have several of the HP 850W PSUs and adapter boards. If I had 220v they would be 1000w. That's a later upgrade. Each PSU has 4 PCIe connectors.
The Prisma has 4 boards with 2 PCIe connectors on each board. According to the posts, each board can run on 1 power connection. I am however going to hook 2 up to each board. This has the advantage of splitting the load on the wire. Mathematically this will cause the wires to heat less, as the Amp load vs wire resistance will be less.
Note, be careful with PSUs that use one cable to feed multiple PCIe connecters. If you can't see individual wires all the way from the PSU their May be junction somewhere. Junctions, depending on how well they are made can heat to dangerous levels.
So what I will end up with is a Prisma split into two power sections. I should end up with about 125w of headroom per PSU.