An outlet is only a connection point. It does not change the sound of anything, just as long as it does its job right. By doing its job right, I'm speaking of it making the connection tight and safely, and carrying the current it's designed to. As long as it does its job this way, there should not be any change in sound.
The 60 cycle AC power coming from your outlet is converted to DC, in your component. If any of the AC is getting through the equipment's power supply, something is wrong.
If the outlet makes a bad connection, then it could introduce noise into the system. A good grade of commercial, or a hospital grade should do this just fine. A good connection should not get hot, or make noise. A hot one is a bad sign. The better outlets can handle more usage, without wearing as quick as the budget ones, that come standard in a lot of homes.
There are a ton of connections that the AC power must pass through just from the transformer, to your home. Then, there are countless connections in the power grid. Not only outlets, power cords just carry the power needed to your gear also, putting these in a similar category. Shielded power cords can help stop RF leakage, that can get airborne. They've been using this shielding on some computer cords, before upgraded audio power cords existed. Also, who knows how many noise generating factories, other facilities, and homes, are tied to your AC power, through the
US Power Grid? There is no proof, that I have seen, of any audio grade outlet doing a better job of this transfer of power, in a home audio system, or any other. Just buy a good quality commercial, or hospital grade outlet. That should do the job just fine.