PS = metric HP. 1900PS is ~1874 "international" horsepower. On B4 fuel and in metric HP, on WEP, the 603A is supposed to do 1750 @ SL and 1850 at ~7000ft. The 603AA is supposed to do 1670hp @ SL. So it wouldn't match any other figure I've seen, other than the 603A @ ~7kft. It's gotta be that experimental unit "C".