Don, thank you for taking time to answer my question (about finding an ideal power supply). I appreciate it. And I looked at those ebay auctions. Maybe I will keep my 0-30v 0-5A Mastech power supply I have on auction now.
I wanted to give a completely different line of thought here, which is that I already have a very powerful and expensive power supply, namely, my modified welder.
It has a sophisticated SCR firing circuit, a microcontroller etc etc etc. It has several modes (all simply programmed in BASIC), several for arc welding/cutting, but also two general low voltage high current and high voltage low current modes. The last two I call the "power supply" modes.
The SCR fired DC that I get, probably has a 360 Hz ripple of about
1-sqrt(3)/2 percent, which is about 13.5%. A little bit of filtering could give me basically a smooth DC of any voltage and power that I may want to get in my "home lab" or to drive big motors etc.
So, maybe some improvements to the "power supply" modes, adding a vernier potentiometer for fine adjustments as well as a filter for filtering out ripple (LC or whatever), would do the trick?
To condense what I said above in one paragraph, I already have a high power power supply, but it may need to be improved a bit for finer control and for better output DC quality. Right now the controls and filtering are okay for rough stuff like welding, but may need to be improved for general bench lab work purposes.
The obvious minus of this supply is that it is in my garage, I need to walk there to turn on the phase converter, etc. (I could easily set up some controls for the power supply, in the basement, to control it remotely by some very simple means, but I would not do it to the phase converter)
The obvious benefits are that I am not using any space (since I already have this welder), I am not spending much money to get a power supply, etc. Plus I can customize whatever I want.
Right now I am in a mode of cleaning out my basement and garage, getting rid of junk etc, but once I am done, I could work on it.