Like campfires, electric hot plates are used to cook food and make chems and other craftable items. Electric hot plates are mostly found inside intact buildings in the Sierra Madre, like the Villa Police Station, and usually have ingredients for recipes scattered around them.
Villa - Northeast of Father Elijah's fountain, go into the building with the hologram vendor. Go upstairs, go through the door to the west, walk west out of the door and into a room where you will find one on the counter.
Villa - West of Father Elijah's fountain, north of the hologram control terminal 01 after the arch.
Salida del Sol South - Turn south from the entrance, climb up the stairs, and walk south along the roof until you come across an arch bridging the gap between the roof and a hole on the wall of the opposite building.
Salida del Sol South - In a room on the south side of the area. The staircase is directly across from a wall in the corner with a hole blown out of the 2nd floor.