By the way, any way you update the PSU will require a reboot.  if you just want to use the USC to see which part number you have, while in the USC at main menu, select Hardware Configuration, hardware Inventory, then view current inventory and then use the drop down box to select PSU1 and it will show you the part number.  if you can pull out the PSU (one at a time so the system doesnt go down), it will say DELL on it in black bold letters. right under the LL's in Dell, there will be a part number there something like XX-03MJJP--xxxxx-xxx-xxxx-Axx If you have OpenManage Server Administrator on the system, open OMSA, click Main system Chasis, then along the top of the screen, select System Components (FRU) to see the listing of part numbers. 
Howdy I have an R810 with two 1100W PSUs. I am in the process of updating the drivers, and there are two models of 1100W PSU on the driver page: 3MJJP and 9PG9X How do I identify the model number of my PSU? Cheers
How to identify PSU model