I watched the video. Both the explanations and measurements are rudimentary. Importantly, as is typical, none show the actual effect on output of any audio equipment! They talk as if these are ready problems. If so, how come everyone is not hearing hum and buzz? And why is it so hard to hear those artifacts as to need these boxes? They show a block diagram of a power supply. Why not show a real one and show its output having the problems they talk about?
Yes, you can have ground leakage between two pieces of audio equipment. A proper test of that would involve actually connecting the two with RCA cable, not just letting them sit with two pieces of audio equipment that are not safety grounded. At one moment he puts his hand on the AVR and the voltage he measures sinks way down. This shows that if you had connected the two together, the measured voltage would be much lower.
But let's say there is a voltage differential. Listen to the gear. Do you hear it? If not, then there is no problem. Indeed, almost every RCA connection has ground currents. It is just that our hearing is extremely insensitive to low frequencies. If there is audible problem, the solution is to use balanced interconnects that don't use the chassis ground at all. Not to go out and buy some expensive power distribution box.
As to DC offset, it can be there and if it is, it usually causes mechanical hum in transformers and such. If you are not hearing that, then you don't have that problem either.
I have done a full video on
audio power tweaks:
