I'm so sorry about that. Is it the PCB that's not mounted? Then that's the dc-dc converter. Its job is to give 24v to the control board, with a 9-18v input. It was an off the shelf part:
PSD-30A-24 Mean Well | Mouser
I think they have the wrong picture up on mouser though. If it doesn't end up working, I'll just ship you another one from Mouser. I used to work at the post office, so I should have known better. You don't want to know what we do with packages. Unholy, terrible things.