There is disclosed a power adapter which comprises an adapter body and a modular connector. The adapter body has a cavity forming a first opening and a second opening respectively disposed on two adjacent lateral walls of the adapter body, a first connecting member disposed on one of the lateral walls and adjacent to the first opening, and a sliding plate member having a sliding plate embedded in a slide and protrusible in said second opening. The connector is interchangeably coupled to the cavity and blocked by the sliding plate to form an electrical connection with the adapter body, and comprises a second connecting member engaged with the first connecting member.