This is supposedly caused by the “polarity” of the ungrounded power supplies. Simply try turning the plug in the socket 180 degrees and see if it gets resolved. The issue is the simple power switch, that breaks only one of those two wires in the circuit. If it breaks the phase, all is fine. If it breaks the neutral, the power still flows into the device.
More precise approach would be to go through the whole chain of power distribution before and making sure that the phase and neutral contacts don’t get flipped between the conditioners, switches, extension cords or whatever you got there.
Depending on where you live, even grounded devices with non-symmetrical plugs might be wired incorrectly - i.e. in Czechia (and France), we have phase in the left hole of the wall socket, while most west countries have it on the right. So I only buy power distributors with Schuko sockets these days, so I can plug all types of plugs in either polarity.
Also, if you ever feel weird electric buzz when touching some devices, it’s the 50/60 Hz AC leaking through the power source into the device, which is generally caused by the same thing - the phase and neutral being flipped around in the power chain.
(Disclaimer - Gemini told me so)