I did have at one time a white paper with the different categories of UPS, but that was over 10 years ago so god knows where it is now lol.
There were basically two main types if I recall with further sub divisions.
The most expensive were the type that converted (rectified) the incoming mains to DC and then used an inverter (and a backup battery) to give the AC output, I think this type was called the full or dual conversion type, the bypass mode was not used via AC in and out, if the mains failed the switching was done at DC level between the rectifier and the battery pack.
The cheaper types used a bypass mode between the AC in and out, this was the type I mentioned earlier.
Then you have expensive types with pure sine wave outputs and some (most) of the cheaper types kick out more of a stepped square wave called an approximate waveform , sometimes this can be important depending on the application.
When designing anything other than single computer/server backup plug and play types it is important to know exactly the topology of the UPS you are intending to use.
If I find (unlikely
) that white paper you are welcome to it, the actual regs may have changed slightly but the physics and actual electrical principles have stayed the same.
