> Or can anybody think of some tricks that may be applicable to make  
> any old
> PS work on 120V DC?

The PC power supplies I am playing with now, double the AC input  
voltage to 320VDC.
They were very unhappy when I tried to run them at 160VDC.

I think your cheapest solution is going to be obtaining a cheap  
converter.  a) 120VDC to 120VAC    or b)  120VDC to 320VDC
The voltage regulation on solution b does not have to be very good.

cc
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