I believe it is a "power supply" that feeds those 2 power relays. They don't utilize a typical power supply since its only drives low current relays so its made with capacitor/resistor and zener (I think). Ive had issue with the circuit getting weak where it doesn't pick one or both of the 24VDC PF relays. Pulling one out slightly and then pushing it back in after a power on was a temp fix. I haven't looked to much into detail before since the customer didn't want further troubleshooting done. The board isn't fun to remove/replace either!
