Here’s how to make a DIY LM317 power supply…
Being able to poke voltages into your projects will help you debug. You can buy an adjustable power supply for $50 or so, or build your own from a kit (another one) Just look for any power supply kit that has a LM317 in it.
You can also build it for $10 using a 9V battery as input and test clips for outputs. This won’t be able to provide a lot of power (cause its just a 9V) but it can go pretty far for testing and debugging
Electronic Equiptment – DIY LM317 power supply – Link.