A: Before December 2016 there was no PSIM SPICE compatibility. Even though PSIM netlist files are similar to SPICE netlist, the way that a circuit is set up and solved is different. For example, only a logic signal (0 or 1) is needed to drive an ideal switch in PSIM. In SPICE, however, the gating voltage must be large enough to overcome the threshold voltage.
As of version 11, released December 2016, the SPICE add-on module integrates a SPICE engine and the ability to read SPICE netlists and models into PSIM. The SPICE variant this is integrated is developed by coolCAD electronics, and is based on SPICE 3F5 and NGSPICE.