Could someone explain exactly how a choke:

a) works -- Depends. If this part of a CLC filter, the choke and the second capacitor form an LC low pass filter. This gives a 12db(v) rolloff above its turn-over frequency. That critical frequency is equal to:

f(c)= (LC)^-0.5 (L in henries; C in farads; f in Hz)

If it's a choke input filter, the choke serves as a constant current source into the load during the time the rectifier diodes are off. This only works with full wave rectification since the choke can't keep sourcing current long enough during the half wave off duration.

b) rings -- Coils are the leat perfect passive component. They include not only DC resistance, but also stray capacitance sinceeach turn is at a different potential from its neighbours. That leads to displacement currents, and displacement is capacitive by nature. Given that stray capacitance and the inductance of the windings, you can expect natural series and/or parallel resonances. When shock excited, the coil will ring just as if it were a tuned circuit (because that's what it is).

c) works correctly/loading -- See:

*Rectifier Applications Handbook* for further details.