790 DT, PSU

PSU (power supply unit) went out last evening:  initially whole PC shut down by APC backup, I maybe foolishly attempted to restart power at the APC, and the PSU blew, strong electrical smells, and now no green light at its back. From what I see on the web, the PSU is goner ~ not a simple matter of a fuse replacement!? I have all the docs,  svc tag, etc  from 2012 orig purchase, including invoice's PSU part number 318-072. On the unit itself are Model H250AD-00;  UP/N: D250A005L;  DP/N:  7GC81.  Searching  Dell for these part numbers turns up no link the parts...  

The 790 DT model I have is one with a thermal switch mounted to the fan housing on the PSU (apparently 790 DT models from 2012 and after used a different board and a PSU without the thermal switch. I ran across something in Dell which said the 2012+ PSU were determined not to need the thermal switch. Dell's Removal guides to replacing/upgrading parts on the 790's with the color graphics are very clear, and they do show both PSU models, with and without the thermal switch. But these guides don't show part numbers so no help there. Doesn't seem to matter about the thermal switch, as long as I can find a proper PSU to put back in. I've done all I can online in Dell's site, trying here for help, before I give Dell a live call (warranty expired some time ago!) Can anyone here help me? Ideally I'd like a get a replacement PSU, but Dell's site comes up with nothing of help.