B737-800 Captain reported on initial descent; the Autopilot Disengaged in smooth air without warning and they could smell potential burning electrical equipment. The flight crew continued destination airport and landed.

Narrative

Just prior to our initial descent into ZZZ the autopilot disengaged in smooth air without warning. I immediately took manual control of the aircraft and assessed the cause finding the left TRANSFER BUS OFF Annunciation accompanied by the Left SOURCE OFF Annunciation Illuminated. My copilot went to the QRH and we ran the TRANSFER BUS OFF checklist without success of regaining power to the associated bus. The procedure in this situation directs the pilots to land at the nearest suitable airport which in this case was our destination airport ZZZ. We [requested priority handling] and proceeded to ZZZ. The NON-ROUTINE LANDING CONSIDERATIONS checklist was also run and the SOURCE OFF checklist was reviewed. Inside the final fix landing Runway XXL the smell of potential burning electrical became apparent. Airport Rescue and Firefighting (ARFF) was requested to be present on landing and the Flight Attendants were asked about the condition in the cabin where no smell was detected.The landing was uneventful and ARFF followed us to the gate as a precaution. We also directed the ground crew to stay away from the aircraft until ARFF had determined there were no hot spots within the aircraft. The Flight Attendant additionally reported after deplaning at the gate in ZZZ that earlier in the flight an oven had smelled of burning plastic and then shut off. This would have happened approximately one hour before the bus off event and was also reported to Maintenance. The crew did an excellent job of managing this mechanical event and maintaining passenger care throughout. When running the NON-ROUTINE LANDING CONSIDERATIONS checklist I decided not to inform the Flight Attendants or the passengers of the situation as we were landing at our destination airport and no further assistance was anticipated. In hindsight I feel informing the Flight Attendants would have been prudent regardless of the fact a diversion was not required.