Help buying a new PSU. ATX12V standards?

They are both great PSUs, as long as its ATX12V it will work fine with a modern motherboard, the EPS specs are for servers and other mission critical systems, its also where the 8 pin motherboard connector comes from. Either one will work quite well. The 650HX is slightly newer and slightly better, but once you get into that range of performance its just tiny differences in ripple and voltage stability that dont affect the end user.

Great, thank you. And yes, I think I will get the 650HX as it is modular also.