I just replaced the Transfer switch on my 1999 Winnebago Cheiftain. Plugged it into a mis-wired 30amp pedestal (don't ask). !2v seemed to work ok, but 2 days later I lost all 12v, so no AC outlets, no refer, Air Con, hot water etc.
Seems the inverter was damaged, just took 2 days to fail completely. Once both items were replaced, everything come back to life except the microwave. That will have to be replace, too.
In my coach, all 12v goes through the inverter, so it it goes bad, that power is not output to all the circuits.