Power cord is an extension of the power supply not of the wall wires. Good well-matched cord will improve the performance of anything that has it. If you can't hear it something is wrong. At higher level one can clearly hear that different cords have different sonic signatures with the same component, not necessarily better or worse. Also, some cords do tend to work better with source components or/and preamp and others with power amps and conditioners/regenerators. My Nottingham turntable's motor has captured cord so I can't upgrade it. Motor controller is a different thing and no substitute for cords, in fact it will benefit from good power cord too.
Anyway, when it comes to turntables I don't know what doesn't matter, it is a very sensitive thing, like it or not or both.
Anyway, when it comes to turntables I don't know what doesn't matter, it is a very sensitive thing, like it or not or both.