Looks like some certifications may differ but units are essentially the same. Given the current sparse availability, should I grab the first I come across (to be used in the USA) or there is a meaningful difference I am missing?
The SSR prefix indicates that particular PSU is safety rated. Seasonic changed their PSU naming system at some point, and depending on where you live, there may be PSUs that utilise the old naming scheme as well as the new one in the sales channel. You can read about the so-called OneSeasonic product naming initiative here.