Sam E wrote
Rod Speed wrote
Sam E wrote

Maybe you've never heard of "switching regulators",

Fraid so.

but I have a lot.

The AC-to-AC converter allows a smaller, lighter transformer
(which I expect draws less power with 0 load)..

You dont know they are AC to AC.

Power to the wall-wart is AC.

Yes.

The load on that converter is a transformer, which REQUIRES AC. A transformer will not work with DC.

Doesnt mean that the wallwart is AC to AC overall, most of them
are AC to DC overall and you dont have to have a transformer in it.

Perhaps you mistake "low power" for "no power".

I never said anything about no power.

The quote I responded to is "They dont have any transformer that uses power all the time". That's the "no power".

Nope.

After writing that I realized that the transformer could be eliminated
by operating the voltage regulator on line voltage (possibly practical
with a switching regulator). That would eliminate the transformer,

Precisely.

as well as the (input / output) isolation which is required for safety.

That doesnt have to be done with a transformer.