Wonder if not a filter could make things worse theoretically ( not I practice as competently design components are not really affected ) .
Like this . I have seen people using isolation transformers in some attempt to reache sonic bliss .
But think of this , passive rectifiers draw “ugly current” from thier power source with a lot of harmonics.
This would not be problematic if the power source impedance was “0” but as soon as this is not the case the current starts to modulate the voltage and you get these current harmonics also in your voltage wave form .
In this voltage is shared by the other things on your network.
Even a big isolation transformer is very small compared the electrical grid and thus have compared to that a high output impedance.
Wonder if not the best “filter” would be a thicker cable to your house from the electrical company
Anecdote time . For a while I lived in the country side . The power grid was rather weak in the area and the local transformer was not a very big one . The heater fan I used in my car during the winter made the mains transformers in my amps hum , due to the “half speed” setting on the fan being a half wave rectifier, hence it made a small DC offset on the AC network .