A portable electrical adapter is composed of a convertible plug and a transformer. The plug has a front part and a block. Two first blades are received in the front part and two sockets are defined at a bottom of the block. Two conductive strips are received in the block and each has a resilient member fixed on a distal end. Two caps are respectively pushed by the resilient members. The transformer has a notch defined therein and two second blades pivotally mounted in the notch. When the second blades are pivoted up, they can be respectively inserted in the sockets of the plug. The second blades each have an aperture defined at a first end thereof. When the second blades inserted in the sockets, the caps are respectively positioned in the apertures to electrically connect the first blades to the second blades and to stably mount the plug on the transformer. The second blades each have a circular portion formed at a second end thereof for directly and electrically connecting with a circuit board of the transformer to improve its conductivity.