If I have the 24 port switch which has 2 power supplies on it, can I have 2 separate UPS battery backups and connect each of the PSU’s to a different UPS? So that if the power goes out it would run off the first UPS and then when that battery dies the 2nd PSU would continue working on the 2nd PSU?
Yes, but power usage would not be sequential it would be load shared so use both UPS power sources at the same time.
Would that accomplish the same thing if the goal is to use 2 UPS so that I can get double the battery run time for the switch and PoE devices? I get about 70 minutes on one UPS connected by itself, so was hoping connecting a 2nd UPS to the 2nd PSU would also give 70 and therefore give me 140 minutes or so now of total battery runtime?
Well, I think it generally would – but with a limitation. UPS run-times are typically not “linear.” There is a certain amount of overhead/inefficiencies in producing the output. You may find, for example, that if you have two UPSs, each of which can yield 70 minutes of run time alone, when used in the manner you describe, and primary power fails, the total time is not 140 minutes, but maybe 100-120.
Having said that, we often do pretty much as you describe. Helps to reduce the impact of power supply and UPS failures. We also try, when possible, to connect the UPSs to opposite “sides” (different phases, actually) of a 240V panel.