Maestro faceplate - does it make a difference?

No.  Don't waste your $$ on snake oil.

If you DO have a problem, address power cables to your DAC first & then an AC power converter (transformer) such as a used Topaz.

a search on here will be revealing

Just use any decent $10 to $15 outlet - Hubbell and others make good solid ones.

You want a solid connection (for the amp) - nothing else matters at an AC power outlet

jubrip - there is no point in wasting time on things that can only work by confirmation bias, not by any known laws of physic or electronics

better to buy some ball bearings, cups and damped tiles to sit your components on...

anyone advocating spendy outlets - much less covers - had better be able to offer some electronics insight into how they could possibly improve SQ

and no, confirmation bias is not a good reason to buy snake oil