An electrical adapter with a replaceable plug structure includes an adapter housing and a plug mounting/dismounting structure mounted to the adapter housing. The plug mounting/dismounting structure includes a carrier, at least one set of contact plates, and at least one releasable fastening structure. The contact plates are in electrical connection with a circuit assembly accommodated in the adapter housing and are exposed on the carrier. The releasable fastening structure is mounted to the adapter housing and includes at least one pair of pushbuttons and at least one pawl section, which is set at a locked position when the pushbuttons are not depressed and is set at a released position when the pushbuttons are depressed in a predetermined operation direction. A plug structure is coupled to the carrier of the plug mounting/dismounting structure with a coupling surface thereof and the plug structure is selectively locked/released by operation of the pawl section.