If you look back quite a few posts, there was a link to an Austrailian poster that used a simple switcher chip (an old one that I nave never found) and he regulated on the input side to the common optimum voltage. This circuit has neither a common positive or negative. Just turned the pot to get the maximum output current. You charge an input cap that acts like a battery so the regulator actually operates in bursts. Since you are less than an amp on the input side, you could easily use any 200V FET and get away with using the primary of a 500 watt 120V transformer (in order to get the resistance down). Running the switcher at 100HZ would let you use regular diodes with higher voltage than low voltage switchers. The common TL494 would do this as long as you protected its power to about 20V, the max gate of many FETs. Do a web search on the application notes and see if you can understand it.