There are so many options it is difficult to know where to start.
From what you said, I’m assuming something that can give you up to 15v at a couple of amps would be suitable. That won’t power a big brushless motor, but would cover any servo, lighting, etc testing. Having a voltage readout is very useful so you can easily set the output voltage.
Here’s one I found earlier..
I have a bench supply I built from a salvaged desktop PC power unit and a Chinese voltage adjuster. Made a plywood box to house it all. Not sure it was worth the effort when you can buy a complete unit for £30