If you have a ground loop issue then it has to do with the fact that some of your components are connected to your breaker box through circuits that have a different resistance than others… this causes a trickle of current running through your system.
For instance, I had a dedicated circuit for my power conditioner and plugged my amp into a shared circuit (a typical home outlet). I had a hum. If I used an extension cord from the same duplex receptacle for my amp it would go away. But this compromised the sound quality. I have two breaker boxes. I had a second direct line put in…adding a circuit breaker for the other direct line in the breaker box adjacent from my first. Problem gone.
Now. As far as sound quality, power cords make a big difference.