Adam,
Yes, the city water inlet has a built-in regulator, however the water leak that you have is from a faulty check valve that is also part of the inlet. So the pressure regulator section of the inlet, has nothing to do with the water leak.
Your original inlet had a 50 PSI built-in regulator, and if you want a little better water flow, I would replace it with the 65 PSI regulator that is now available as a replacement. The other alternative is to replace it with an inlet that only has a check valve and no regulator, and always use a high flow Watts adjustable regulator at the campground facet to control the water pressure. This setup will give you the highest water flow possible.
Gerald