When I dare to use an
A) electric blanket, or a electric frying pan set on "low",
at the same time when there is a
B) UPS computer power supply, or Ham radio power supply
also turned on anywhere in the house, the power supplies hum most
worryingly. One must make a choice: A) food, warmth, or B) fun.

What is the name of this waveform resonance with the current limiters
of A phenomena? Is there some kind of filter I can apply?

That sounds to me as if you're running into a "harmonic currents"
issue. This occurs if you have something connected to the mains which
draws current in a nonlinear fashion (i.e. current drawn is not
linearly related to the instantaneous value of the voltage sinusoid).

In my experience, the commonest cause for this is a device which uses
a triac "chopper" to control the amount of current being used. Such
devices "switch on" partway through each powerline cycle (120 times a
second), so the current jumps from zero to a fairly high value. The
sudden jump creates a load on the line with frequency components at
harmonics of the 60 Hz powerline frequency... hence the name.

The devices you indicate (electric blankets, frying pans), and light
dimmers are notorious culprits.

Some of these devices may draw current in an asymmetrical fashion...
e.g. they might use a half-wave rectifier diode, and thus draw current
on only the positive half of the AC cycle and not on the negative (or
vice versa). "Light bulb saver" discs (little disc-shaped diodes that
go into a light socket before the bulb) do this. In effect, the
asymmetrical load creates a DC offset on the voltage "seen" by other
devices on the same circuit.

All of these "bad loads" can cause transformers in other devices to
start humming or buzzing. Toroidal power transformers are
particularly subject to buzzing if there's an asymmetrical load / DC
offset on the line.

I don't know of any good way of filtering out this sort of problem...
an isolation transformer can help somewhat, sometimes, but it's an
expensive solution and I don't think it's very effective.

If you've got really severe humming/buzzing with something as simple
and low-wattage as an electric blanket, , I'd be a bit concerned
that this might indicate that there's a problem in your house
wiring... overloaded circuits, a bad or loose connection somewhere, or
even a loose or open neutral. The latter is a dangerous situation.
If you should notice lights getting brighter, or appliance motors
speed up, when you turn *on* a light or appliance elsewhere in the
house... then you may have an open neutral and should call the power
company immediately. I've had this happen twice (squirrel chewed
through the neutral wire in our building's drop from the pole
transformer), and PG&E always reacted immediately... their dispatcher
said that they consider a "low voltage / high voltage" situation to
require immediate action.

You might want to have an electrician check out your house wiring.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!