Retimlap,
Your boat was never offered from the factory with shorepower...which isn't to say somebody didn't "attempt" it. I worked on a boat once in Tarpon where a guy had pulled 120VAC off his battery charger to power up outlets in the cabin when he plugged his charger into an extension cord. Not the correct way!
If there is no shorepower inlet, the PO may have been using an inverter to provide power to the outlet, which is a completely acceptable way to get 120VAC. Is there any evidence that one exists, or existed? I'm assuming the outlet is somewhere in the cabin sink area. Let us know.