Harbor Freight DVMs are available free from time to time. I've repurposed a few and still have some in original packaging. Connect one as "Ammeter" and one as "Voltmeter." Kinda large for a small power supply, though. There was a section in the ARRL handbooks for a few years that showed a commercial DVM stuck to the panel. That was more involved than putting 2 cheap ones in. I have one that I carry to hamfests without leads, just to check transformers and chokes.
Ted, KX4OM