This stuff dates from the 30's and early 40's.
The porcelain outlet and box were common in barn and outbuildings due to the nature of a barn's corrosive conditions. They were either connected with K&T, early NM cable, or lead-sheathed MN cable.
I've seen these in an old barn, and it was wired with early black NM cable. I didn't have the liberty to salvage any of it.
I have a switchplate exactly like that one in my stash. It came out of a 1930's basement.