This is an interesting topic. I say bring back Mercury Arc Rectifiers - I saw one used on the Manx electric and it looked like dante's inferno. You used to be able to see the one at the Crich tram musem in a lttle shed half way down the line. On the modelling front, one of those arc welder flashy thinks in a shed would do nicely.
Anyway, Chief Simpleton here, about to incur the wrath of wiser men. Having read and inwardly digested I offer the following cheap generalisation of an SMPS.
A device which takes sinusoidal AC and converts it to a high frequency PWM square wave signal before rectifying it to DC and removing any residual ripple.
:-X