For high current using PC power supplys can be cost effective, a person may have one or two lying around not being used as compared to buying a transformer and large value capacitors.
I have attached a concept drawing on how the voltage can be varied and also power input switch allows selection of low high voltage less heat dessipation at lower output voltages.

 

Hopefully I'm not hijacking this thread but can anyone tell me what I'm doing wrong on these attacments? they look good on my computer but once uploaded there are lines missing
Thanks

 

Pich, you're not doing anything wrong. Once you click on the attachment, you have to click on the window that opens up in order to see it full size. The pic is too large to fit in the window, so your Web browser tries to scale it down to fit. Clicking on the image will toggle between scaled and full-size.

 

I still like the idea of sourcing more current at the lower voltages. Is there perchance any means of switching the switches? Rephrased: might there be any way to parallel the 'puter supplies for lower voltages and higher current, then series them for higher voltage with lower current limit?

As long as the supplies are isolated you can series them. Paralleling
would not be a problem.

At Vicor we build a 4KW (3 phase) programmable supply using 2 MegaPACs. http://www.vicr.com/products/configurable/mpfamily/
Each output of the MegaPAC had either a 12V or 24V isolated converter.
There was a relay bank that could series and parallel different groups of
converters to get different ranges. The MegaPAC outputs can be trimmed down
to 10% of its nominal value. In a given range you are current limited.

The supply did apx 400V @ 10A or 12V @ 200A. It was 3 phase and had power
factor correction. It was used to burnin Vicor converters.

If you could build a bunch of isolated adjustable DC-DC converters you
may be able to do a similar parrallel/series arrangement to get high voltage/low current
and low voltage/high current.

Also a modular design would allow you to easily expand the power/voltage/current
ranges.

(* jcl *)