It's a half bridge BJT resonant circuit, the smaller transformer is drive. The control IC apparently starts and stops operation, to kickstart it and presumably to control frequency and thus power.
The split-bobbin construction provides leakage inductance, making an LLC resonant converter. This is why the output is FWCT rectified, with no filter choke.
I can't tell why they put extra diodes in there, or what the one resonant cap back to the AC side of the FWB is doing. I think that must be where the PFC is coming from. The 12uF filter cap is much too large to give low PFC by itself.
Tim