Switched mode power supplies and led lighting chuck plenty of high order harmonics onto the mains supplies. These tend to alter things like the power factor correction and in a 3 phase system neutral loading. Filtering these out requires large and expensive passive filters and no domestic mains strip is going to manage that.
Back in early 90s I was working as an analogue design engineer on high speed cassette copiers. These got shipped all over the world and to ensure they would work on any provided supply we used to test them on a variety of "dirty" mains sources including generators, ups, isolation transformers and harmonic generators that used badly wound transformers to create electrical noise. I can confirm that quite subtle changes can occur when connecting audio equipment to ropey supplies. I would describe this as an increase in the noise floor and audible "thickening" and distortion of the sound. Sticking a 'scope on the power supply, the regulation tends to go out of the window and the increased ripple decreases the smoothing effect of capacitors. Anything with a linear power supply will be worse affected, as the transformer tends to act as a big inductor in a tuned circuit and creates quite measurable transient spikes when using an Electromagnetic probe.
As I said however, removing this clutter is quite hard to do and requires high current tunable filtering. I would seriously doubt if any consumer level equipment has the ability to do so.
Wifi, 4/5g and other low power radio signals will not affect a mains supply. You need a high current source of interference to produce any measurable effect.