Eletrical Doodads were first introduced in the Reign of Giants DLC. During the Early Access phase of the Hamlet DLC, they were then retroactively added to the base game to allow Wagstaff to craft his specific items.
Electrical Doodads used to be crafted from the Refine Tab.
Electrical Doodads were initially added to make it harder to craft crucial objects, like the Alchemy Engine.
Per Wagstaff's quote as well as its appearance, the Electrical Doodad is a diode despite its spawn code referring to it as a transistor.