US. I’d be surprised if anywhere was allowing more than 80psi.
20psi is really low so this value may have different variations. I’m on a well pump and before I replaced it I was getting down to 20psi. It barely dribbled out of the 2nd floor shower head. I now have the pump set to 60/40 with a 50psi restriction valve. This seems to be the sweet spot.
I’m not in plumbing and won’t know how to look this stuff up.