I've seen plenty of campgrounds which charge extra for 50a over 30a but I've only stayed at one campground which used electric meters and charged me for usage. Of course, their math failed and I had to check their homework to get my charge right. It was not operated as an extended stay camp. I was only there one week - in Schulenberg, Texas.
Mainly in the North East. Usually on an extended stay. Have had many CG owners say the electric company or zoning and price of meters dictates what can and will be done. I will not stay in a park where they wanted me to get the electric in my name. Was in talladega, AL.