Vintage/Antique? Ceramic Porcelain Electric Wire Outlet Cover With Plug 8358

Description

Up for auction is a vintage (perhaps antique?) porcelain/ceramic outlet cover with built in plug.
-It is in overall very good condition. Don't see any chips. Just a little dark mark on one side. Probably would clean up.
-The plug is attached but could be removed with the screw in the middle of the face plate.
-Unsure of the manufacturer, but there are two markings on the back. One is the number "8358" and there is an "M" inside of a triangle.
-Ships Priority Mail.