I found this high pitch hum/buzz too. I have a supa-charger and joyo 2 power supply. This is part of my chain: B9 -> C9 -> Micro POG.

The pitch has to do with grounding. I think the Supa is more “isolated” than the joyo. When I have my C9 and Micro POG in the Supa and the B9 in the Joyo, I have the hum. Since I have the three devices and only two 200mA sources per device I had to test with a process of elimination puzzle. This is what I found…

If I have the B9 and C9 in the same supply and the POG in the other (doesn’t matter which), the hum is gone unless I touch the metal cable casings of the B9 output and C9 input together, then it’s back. Very strange. Since the combination I have doesn’t allow all three 200mA devices into one supply I can’t really test further.

I’ve resorted to running the C9 and POG off one of the supplies and the B9 off the provided power supply/wallwart from the wall. Since the B9 seems to be part of the issue this seemed to make more sense.

This makes me think that if I cut the ground on the cable from the output of the B9 to the input of the C9 that I’d probably be golden as far as those pedals, but then I’m sure I’d run into a mess with all the other pedals I have after them that are across the two supplies.

Yeah, hornets nest.

I might try eliminating the joyo and going with a second Supa Charger to see if two higher quality sources makes a difference, but I don’t have that option right now.

The reason I think it’s the supply and and isolation is the Supe is regular 120v with a C13 type cable and the Joyo is a wallwart canon type in. The Supa seems to be more grounded and AC than the Joyo. IOW, the joyo might have a single input transformer before it hits the individual output transformers. The Supa might be more isolated on the input as well as the output. Just a thought.

Hope that all made sense.