The PulseMH need an OCV about 220..250V and an inductive impedance (to control the lamp current; so lag type - to ensure the ringing after current zero cross sum with the nearly peak OCV at that point help to reignite the arc), so it depend on the mains voltage, what concept the ballast may use:
- CWA is not a good type, as it use capacitance as the ballasting impedance (it is the lead type). That mean, then the arc is not able to restart immediately after current zero-cross, capacitor does not allow so large ringing. Consequence is early cycling.
- HX autotransformer: Universal in terms of available mains voltages (as it is a transformer - so may convert anything to the required ~230V OCV) and the output impedance is inductive (= leakage inductance)
- Serial reactor (coil): Most efficient and the smallest type (as it have to implement only the impedance), but feasible only for the mains voltage in the required OCV range (only 240V for US/Canada and standard 230V mains in "230V world")
For the HX autotransformer and the serial reactor it does not matter, if it is NPF or HPF, as the difference is only in the presence of the PF compensating capacitor parallel to the mains side (on HX usually between the highest voltage tap and the neutral, it's effect is then correctly "transformed" to the used voltage level). It does not influence the behavior towards the lamp (unless it form the current path for the ignitor pulser - e.g. for SN57-like ignitor circuit)
I found out that the ballast in my fixture is an R-NPF ballast. From what I found, PSMH uses CWA or HX-HPF ballasts. 
Wow, thats a lot of info! So what makes an R-NPF ballast incompatible with PSMH?
