I'm fairly sure is a zero voltage switching converter with active
voltage clamp. The series inductor and the 4uF capacitor form
a harmonic filter. The resonant switching circuit is the capacitor
in series with the upper switch, the primary inductance of the
transformer and the capacitor in parallel with the transformer.

So it can be devolved into a single switch feed forward converter
function from the lower switch and resonant energy recovery by the
upper switch... which results in a quasi push-pull output.

Search patents by E. Miyata in USPTO for more details.

Considering it's purpose, I'd expect this design's output power
is probably in the neighborhood of 750W. Don't confuse this with
the name plate rating. Of course the designer didn't consider
ICAS service so YMMV.