The Tier List is a good list, but it really judges power supplies in more general terms for a PC enthusiast market, weighing component quality, value, and warranty. It’s definitely a good place to look if you’re considering deals on a desktop build, but it doesn’t offer the most insight into the things we’re looking at here.
Seasonic has been at the top of my list for brands to look at from their history of reliable power supplies, but I’ve noticed all but the 1000w units are still 20 amp for the 5/3.3v rail. I saw some other discussions of this on the forums and @Stux mentioned using a Corsair RM1000x for his 24 disk build. Looking at the manual, all the models in the RMx series are 25 amps on the 5v rail, with max output of 150w starting with the 750x model (the RM650x and 550x are 130w). The Seasonic Focus GX tops out at 125w on the 1000w model, with lower models being only 100w on the 5/3.3v side. I’ll look at some other brands, too. Also the number of ports for disk power cables will be something that I’m looking at.
Okay, call it a NAS, or w.e. 
It’s not a “server chassis” with redundant hot-swap power supplies, but something that takes up 6U on a rack and can accommodate water cooling isn’t really just a “NAS” at that point I’m sure you’ll agree. It’s made to use standard ATX supplies so you’re not tied to a small market of 1U or Flex options.