Hi
I would guess that I have a couple hundred power supplies of various sorts running around here that *could* be used in design work.
Roughly 2/3 of them are of the wall transformer variety. I never throw them away. The gear they came with goes into the trash, but the power supply goes into a big bucket. They have a wide range of power ratings and voltage levels. Some are regulated. Some are simple bulk supplies. I also have an inventory of them that I bought over the years on places like eBay. I usually look for auctions that are selling a bunch of "new in box" supplies cheap. Sometimes I win the bid. Mostly I loose.
I have a number of high power supplies running up into the "several KW" range. They don't get used much. They are so heavy that they are hard to sell. Most of what I have was "free if you pick it up". If you are doing a high power amp, having a 0 to 50V, 100A variable supply is pretty important. Finding one when you need it is tough. If you are powering up surplus gear, a lot of it runs on 24 to 32 V. Having a number of 35A variables around to fire up the various boxes in a system lets you sort things out much quicker.
Analog meter based bench supplies for some reason unknown to me went out of fashion ten or twenty years ago. They started showing up for ridiculous prices. As a result I have a few dozen of each of several models. This was the same sort of deal. Bid on auction lots of a dozen or two and win a few auctions. They work fine with analog meters. They are 0-15 or 0-30V units in the 50 to 100W output range. They are very useful for powering up just about anything you can imagine. It also is amazing how many of them you sometimes need when getting a circuit running.
On top of all that I have a handful (< 20) fancy multi-outpt supplies. They are nice in terms of bench space. They also are good for bringing up all the supplies to a circuit at one time. Having everything adjustable and tracking comes in handy sometimes.
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None of that is very helpful is it? It simply demonstrates that over a 50 year period you can accumulate a lot of junk. Accept that if you stick with this, you also will accumulate a lot of junk. The big take away - don't spend a lot of money on power supplies. They will come along cheap over the years. I am quite sure that none of my supplies cost over $50. People claim that you "can't find that stuff here". I have lived *many* places over the years. Each place has been a "there isn't any around here" location. I have always found gear available. The difference is that you need to put effort into finding it. When it shows up, you have to go get it right now. There is no waiting and deciding. There is no picking and choosing. You grab the whole lot and haul it away. They let it go because *they* didn't want to bother hauling it all away ....
Still not really helpful ..
Out of the empire of gear, the most useful stuff are the wall transformers. They are also the easiest to find for free. They are not very exciting or cool. Pretty much every circuit you design will have an on-board regulator (or several of them). That's the way things are done these days. A wall transformer will feed a 78L05 or 78L12 just fine. If you pay more than 10 cents for the regulator, you need to spend more time shopping ...
I would suggest that a pair of 0-30V variable supplies with meters would get you going on anything that the wall transformers will not handle. Past that, grab what comes along.
Bob