I seem to remember on the psd stand alone it was a facet pump running a constant 0.5bar. Still managed to blow both outlet bearing seal springs under heavy use, though it would have been seals but PSD glued the seals in, my charger was getting long in the tooth though after far too many rebuilds. My engine could rev too quickly upto 8k for the charger, which the charger didn't like too much.
On a normal engine, a stand alone oil system is worth its weight in gold i reckon.