Good topology for a capacitor charging power supply

[Circlotron]

Simple and resonant? An inductor, diode and switch in series. Or just an SCR and inductor. The cap will charge in one half cycle of resonance of the LC combination. Whatever DC voltage is supplied to the input side, the cap will charge to double this voltage. The charging current is a half cycle of a sine wave. You may need a fairly large inductor though, say one out of a mercury vapour street lamp.