> I set up my own home network with a Vertiv Liebert Li-ion UPS a few years ago and was thinking about how inefficient the whole process is regarding power. The current goes from AC to DC back to AC back to DC.
With double-conversion, generally yes.
I recently ran across the (patented?) concept of a delta conversion/transformer UPS that seems to eliminate/reduce the inefficiencies:
The double-conversion only occurs when there's a 'hiccup' from utility power, otherwise if power is clean the double-conversion is not done at all so the inefficiencies don't kick in.