Right, so I needed an ammmeter for guitar pedals. Why just for guitar pedals? Because they all have standard center negative, 2.1mm jacks, and they all use 9V. Easy, just buy a panel mount ammeter on Aliexpress:

With that sorted, we need an enclosure. I sized this for the meter, a 9V battery, and two jacks:

Wire up the guts, with the addition of a 9v battery clip and a DPDT switch:

Button it up with some M2 threaded inserts, a bottom, and some labels. Put some velcro on the bottom too, because pedals:

Neat! It's done! Let's test it out:

There we go! Now I know how many pedals I can put on a single output on my power supply. What the hell, Strymon?