I am not clear whether you are referring to an AC adapter for the mic or if you are using the Canon coupler with your Canon and an AC adapter with your phone?
If the problem occurs with the microphone using an AC adapter, it is likely an issue with the adapter. Wired microphones require very little power for the built in impedance converter, preamp, or bias source for a condenser type element but it must be exceptionally clean because of the low signal level involved. Very few aftermarket adapters provide sufficiently pure DC for this purpose but if it was supplied by the manufacturer it should be.
DSLR cameras and smartphones typically have a fairly high impedance audio input making it far more likely to pick up electrical noise in the environment, this is why professional audio is done using XLR connections with balanced low impedance lines to reduce this sort of issue. There is a slight chance that your adapter cord itself is picking up noise and coupling it to the microphone. Most, but not all, modern devices sense when voltage is present rather than a mechanical switch to go between battery and line supplied power when an adapter is plugged in. If your microphone works this way, plug the adapter into the DC input socket of the microphone but not into the AC outlet and see if the interference still shows up.
If you mean there is an issue when the camera or phone is powered by its AC adapter, then the problem is more complex because it may be from the adapter for these devices not being clean enough for good audio coupled with a microphone that has lower than typical output requiring higher gain. Very few camera or phone power adapters provide any sort of ground to the house ground system and with these any noise appearing on the line is imposed on the device being powered by the adapter. Depending upon the noise sources, plugging the adapter into an isolation transformer will help because the shielding between the primary and secondary in these devices greatly reduces the transfer of "garbage" on the line from primary to secondary. Unlike the fairly clean AC of 20 years ago, the AC delivered within a house is very dirty due to all of the very cheap and poorly designed switching type supplies used with almost all current consumer garbage which creates all sorts of interference and transfers that to the line. You may be able to turn off the offenders in your own home when using a video setup but you can't do this if recording elsewhere. IF you have to have something other than the internal battery power when using the system remotely, you may need to investigate a good quality sine wave inverter with its own internal battery to power your AC adapter thus avoiding AC line noise via direct connection to the line.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
