"mm" wrote in message
...
I was looking at an FAQ for some small appliance that runs or
recharges from an AC adapter, a black box that plugs into the AC and
lowers the voltage to 12 or less, and maybe changes it to DC.

And it said this was safe, and I too have been assuming these were
safe, but...

Has anyone heard of a short in one of these adapters that sent 110
volts to the thing that was supposed to charge or run off the
adapter???

That would be unsafe, if it happens.

I have used many of them for year for my electronic projects. I stripped off
the plug on the end of the wire and plugged the wire directly into my
breadboard. A couple times the wires came out and shorted together which
blows the internal diode bridge or the primary winding opens. The primary
winding is made of fine wire on these small transformers and acts as a fuse.
Never any smoke, fire or oders from a failed one.

Some of the new ones have switch mode power supplies. The secondary is still
isolated via a transformer and feedback to the primary switching circuit is
through an optoisolator.