Thanks guys. You've been most helpful. I think I'll take a chance an order one of those Dell 875W PSUs.
My main interest in changing the PSU is to be able to run my R9-290 that requires 1 x 8-pin and 1 x 6-pin. I had the card installed temporarily... had to remove the top drive "plate" (or whatever you call that section of the swing down bracket that holds the upper drive) to allow room for the card's PCIe connectors. The case is quite narrow. The orig. 575W PSU with PCIe adapters handled the card for test purposes, but I wouldn't want to run maxed out with that PSU.
Btw, mine has the Xeon 3.2/3.4GHz W3670 6core/12 thread CPU and 24GB RAM. There must be a thousand of these Precision workstations being sold cheap right now. I see them everywhere.