I'm wondering how modern turbo systems work at altitude:

Another (aero) engineer at work was telling me about prop aircraft turbos and how they were originally significant because the piston engines could attain the same power regardless of altitude by using boost.

In modern cars, do turbo systems boost to the set pressure and produce the same WHP at high vs low altitude, or do they pay a penalty? I'm sure it could change based on the setup specifics, but I'm wondering if local Evo/Sti/other FI car owners here in Salt Lake City would be running the same times they would run at sea level while my NA car pays a heavy penalty at 4000ft.