What is presented is an extension cord with a convertible electrical plug end that can be connected to grounded and ungrounded power supply outlets. The extension cord comprises an extension cord and a plug end and is configured to transmit electrical power. The plug end is connected to the extension cord. The plug end itself comprises a plug body, plurality of prongs, flap, and ground contact. The protruding prongs are connected to the plug body and configured to couple to the outlet. The flap is movably attached to the plug body such that the flap can rotate relative to the plug body. When the flap is in the closed position, the plug end can connect to a grounded outlet. The ground contact is configured to releasably and electrically connect the extension cord to a ground potential on the outlet.