Prinsloo is indeed of Dutch origin. It is composed of the Dutch words prins "prince" and archaic Dutch loo, which signifies a clearing (i.e. open spot) in a forest. The surname is extremely rare in The Netherlands nowadays, with 5 bearers in 2007 and 0 bearers in 1947. This seems to indicate that the 5 bearers must be immigrants from (South) Africa. As such, this is definitely a typical but old Afrikaner surname.
"How do you pick up the threads of an old life? How do you go on... when in your heart you begin to understand... there is no going back? There are some things that time cannot mend... some hurts that go too deep... that have taken hold." ~ Frodo Baggins