Don’t get me wrong, if you have a good jam or preserves it’s totally fine on a sandwich, and I wouldn’t turn my nose up at it. However, peanut butter doesn’t really need the help, and the extra sweetness from jelly is totally unnecessary. Toasted bread and peanut butter is all you need for a quality simple sandwich.
I tried peanut butter and jam because I always heard it being talked about in American movies (am European). It was a waste of both imo. Peanut butter and chocolate sprinkles is the way to go if you must add something to peanut butter. Jam is best on its own.