In some embodiments, the present invention provides an independently tightening collet surrounding each socket for each of a plurality of corresponding high-electrical-power prongs, wherein the collet is loosened for normal (low-insertion-force) insertion and withdrawal of the plug from the outlet. Once the plug is inserted, the collet is tightened, providing a high-contact force to lower the contact resistance and to help keep the plug from coming unplugged. In some embodiments, the plug is not “locked”, in that a tension force pulling on the plug will overcome the contact force at a point before the plug or outlet is damaged, and the plug is allowed to come unplugged. In some embodiments, engaging the collet will also provide a wiping or sliding motion between the prong and socket for each connection, thus wiping at least some dirt or corrosion away and providing a lower-resistance better electrical contact.