A more clear picture would help.
I'm suspicious of it being a USB port as the wire/cord in the background 'looks' like it is either a two pole DC connector (typically not used with 5v USB multi wire type connections) or it could be an audio connector of some sort?
A clear photo of the connector socket in the plate and a photo of the connector on the wire (taken apart showing ends) would be helpful.
Could be an IR wall plate. I discounted that because the OP said "wall plug" and I took that to mean something actually plugged into the rectangular port. The OP's picture is to fuzzy to tell. An IR wall plate has a reddish plastic lens covering the port and you cant plug anything into it.
It's for the stereo system remote. After installing new batteries and turning the stereo on I used the remote pointed at cover plate and it turns off stereo. But the dealer could not tell me what it was. I knew I'd get the answer here