Just wondering...

Is it OK to leave the AC adapters used by many gadgets plugged in while it
isn't connected to anything? For example, AC-DC charger for a cellphone
left plugged under my desk with the end of the cord on the desk in a handy,
out of the way location.

I assume that an AC-AC adapter should be OK, but an AC-DC might have
problems since it has the rectifier and filter caps always trickling a bit
of current through them. Even worse would be the switching supply of a
laptop when the laptop was elsewhere.

Other than the obvious electrical spikes that could damage anything, is it
bad to leave these things plugged in?