I must say that Joe Cohen once did a demonstration of a very substantial aircraft aluminum wall plate and similar surround over the wall plug of the pc that was shockingly better. I never bought it, however.
I did buy the IsoClean wall outlet. I also found that a single Acoustic Revive QR-8 in the center face greatly improved it. I now merely put a QR-8 in the center of the existing plastic wall plate and find it improves the sound somewhat.