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The second most important piece of equipment you can have as an experimenter is a good, bench style, power supply. And here, there are many surplus choices available from places like Ebay. However, I would stay away from the bargain store brands, and get a name brand that you might find in a lab. The good ones are almost indestructible, and will serve you for many years. I am partial to Power Designs (Above). The one that I have has been with me for over 30 years, with never a failure.

You will end up using this supply for all kinds of things, not only to power your projects, but to test parts, motors, relays, lamps, etc, you remove from surplus equipment. It can serve as a battery charger, and as a battery eliminator for repairing battery powered items.

Make sure whatever supply you get is an Analog Supply, NOT switching (as in a pc). Switching supplies have load requirements (Not good for experimenting), and will introduce noise into your projects, especially audio. They are also prone to "Melt Down", and not as tolerant of overloading. Often switching power supplies also offer less line isolation - A big no-no.

While you will most likely acquire many power supplies over time. I suggest that you start with one good, single output supply. In addition to that, if you do a lot of breadboarding with analog components, next would be a Tri-Output with Tracking. Finally, if you do much car electronics or audio, invest in a good 12 volt analog, regulated power supply of at least 10 amps. There are many more specialty needs. Aircraft use 28v at high current. If you like to work on large robots, you may need a High Current variable supply (15-20 amp). Telephone equipment frequently works at 48v, etc. But, this will get you started.

Some features to look for, or not:

This is my main and most used power supply. It is a Power Designs model 5015T. It outputs 0-50 volts at 1.5 amps. I have used this supply for over 30 years with no problems. I use it to power just about everything, to charge oddball batteries, and to check out surplus treasures. I love this power supply!! It only has one meter, switchable between volts & amps. As mentioned elsewhere, I have a Separate digital panel meter permanently connected to this and mounted under it on the bench. I normally leave the analog meter on current. It has a completely adjustable current limit with a front panel knob. I keep two long leads with alligator clips attached to it, as well as my aforementioned Power adapter cable. Other than occasionally wishing for more current capacity, this supply simply fills my needs.
This supply is also a Power Designs. A model TP325. It has three outputs. One is separate and supplies 0-6 volts at 5 amps. The other two have a common return and supply Plus and Minus 0-32volts at 1 amp. It has a meter for each output selectable between Volts or Amps. Note the tracking switch in the center that allows the two 32v supplies to be adjusted together. The current limiting is screwdriver adjustable (frown), but at least on the front panel. It also has adjustable Overvoltage shutdown. I normally use this with a Pre-made 5 conductor cable with banana plugs, to connect to a Protoboard. I acquired this about 20 years ago, and even though It fell off a moving truck once (and has a huge dent in one side), it keeps on working fine.
This is a shot of the left of my big Protoboard design station. Up in the upper left is a built in power supply that provides one 2-10 volt output at 2 amps, and two 5-30 volt outputs at .2 amps (Unfortunately not tracking). The meters are for current and voltage, and can be switched to any one of the supplies. Since this is built in, I can power my latest masterpiece without the need of wires or cables.
Finally, I wanted to mention AC Supplies. I do not have a real good adjustable AC supply. This is my AC Variac, which is very useful for testing old equipment. One of these is definitely a good addition to any shop, especially for repair work. Normally if I need some type of AC I will jury rig something. But, Although I will cover the subject thoroughly elsewhere I do want to point out that this is a Variac, or Autotransformer. It is connected directly to the AC Line, and offers NO isolation. Be very careful using these, they are NOT isolated!

There are many more power supply options, and as I said you will most likely aquifer a few more. I just wanted to give some idea of where to start, and what is needed for a good setup. All of these are available surplus, and I have had incredible luck with Power Designs. I also have a number of single output supplies which are handy, but not real necessary. And 12 volt supplies likewise, are readily available, used or new. Check out an Amateur radio supply, or a CB shop. MCM Electronics has a lot of good values on these, but be careful of the quality! A note also, if you want to experiment with tubes, you will need a Variable High Voltage supply. I know B&K makes a good one I have used before. Again, check out Ebay. And that's all there is to that!