With any DC device designed to be fed with an AC source you can feed it
with DC - provided you take into account the voltage drop through the
rectifier. And given the poor regulation of most AC wallwarts this is
rather easy to calculate.



That's really not always true, I had an external modem years ago that
would only work properly from an AC output adapter, and a couple
different bubble lamp things and kinetic sculptures that used
synchronous motors and vibrating air pumps, those devices all required
12VAC and would not work correctly from DC. I've built a few digital
clocks that also require an AC output wall wart because they derive the
timing from the line which is much more accurate long term than a
crystal though since those are not a commercial product I can't really
count them.