This is from Audio Research.

Let’s say you have your audio components plugged into various standard duplex electrical outlets in your listening room…
And not using fancy aftermarket receptacles or power conditioners…

And you are not using both sockets of the outlet where you have your power amplifier plugged in, for example.

Or you are not using both sockets of the duplex outlet where your preamplifier or front end source components are plugged in.

1. Fire your system up and play a few demanding tunes you are intimately familiar with…
2. Now turn your amplifier off and plug it into the unused socket in the same duplex outlet receptacle.
3. Turn the amp back on, waiting a couple minutes for cool down if it is a tube amp.
4. Play the same songs and observe whether the sound is more relaxed, pure and dynamic or less so.
5. Use the socket in the outlet which sounds better.
6. One of the two usually sounds noticeably better; believe it as this is a common, repeatable empirical observation and result.
7. Repeat the process with each component connected to a single-use outlet, reaping the cumulative sonic benefits of the best connection in each outlet box.

In addition, you can swap cords from components sharing the same duplex outlet, from top to bottom and bottom to top sockets, and you will likely have a sonic preference here as well.

Feel free to comment and share your results.

Happy listening from all the ears at Audio Research