It's probably the .380 or 9mm kurz you heard about. Walther experimented with an enlarged PP in 9mm luger in the 30's that they called the MP, but there were only a couple of prototypes made before they realized that it wouldn't work in a blowback pistol. There is no way to put in a strong enough recoil spring to handle the pressure generated by the 9mm and still be able to hand rack the slide.
Yeah, the PP Super was a more successful attempt by Walther to up the power of the German police pistol after the Munich terrorist attack during the olympics in the 70's. I think ballistically it was comparable to the 9mm makarov round used by the communist bloc but, to the best of my knowledge, the two rounds are not interchangable. I always thought that this was a sexy looking pistol... if that descriptive can be used on a gun... Does that make me a wierdo?
You are correct .... the 9x18 Ultra/police and 9x18 Makarov are not the same round... Do not shoot the 9x18 Makarov in a PP Super....
By the time the PP Super was on the streets.... police already decided to go with the bigger 9x19mm, or the PP Super might have been a bigger hit.
The PP Super is sexy.... and almost as good looking as the P5c