I recommend starting with a good benchtop supply that you can count on. If you build your own it may function ok, but will it have voltmeter and ammeter, will it have multiple outputs, will it have current limiting and constant current modes? These are valuable features in my opinion. For my bench, I bought surplus DC power supplies wherever I could (ebay, dovebid, local companies etc.) in brands like Hewlett Packard and Fluke/Philips. Have a look on Ebay for Mastech brand supplies, they seem like very good value. I see one that is a triple output (3 different DC supplies in one), 30V/3A with all the good features for only $168. That's quite good if the unit is reliable. Perhaps others can chime in on reliability of this brand.