Ok so I've done some searching and I'm a LOT less confused. I found this
Silverstone redundant PSU, but its only a 460W and I'm thinking that I'd like a bit more breathing room. I also see that this looks like it'll fit in the same formfactor as a standard ATX PSU. Any suggestions for a double stacked one? I guess I could also go for a 3U or a 4U enclosure.