I'd always been very much in the "how can a 1m power cable make a difference compared to the wiring in your house/street etc" camp, but here's a bit of reading on the subject that at least explains a bit of the rationale. The articles are written by a power cable company, but even my sceptical brain can see a degree of sense to it.
https://www.gcaudio.com/tips-tricks/electrical-delivery-systems-overview/
https://www.gcaudio.com/tips-tricks/why-power-cables-make-a-difference/