I cannot tell without /s, but yes, who designs like this, lol

> Asrock Rack C246 WSI Mini ITX

Who do I have to kill to get one :)

In other words. I asked if A should lead to B. You answered "A leads to Not B" :)

> If it expects a real grid-like sine wave and doesn't see one it will reject it, regardless if the load would like it or not.

But why would it require grid-like sine wave and not go along with whatever is the source, provided source can still be used to charge its batteries? I saw no answers yet, and this "why" is the very key to the discussion.

> Your run-of-the-mill UPS is likely to either be offline, which forwards the input to the output,

This one surely should "like" simulated sine wave as a source and don't drop to battery?