A system comprising a first device comprising a first electrical connector exposed at a first surface, the first device including a first set of electrically conductive prongs arranged according to a first configuration, a second device comprising a second electrical connector exposed at a second surface, wherein the second device is an electrical adapter including: an electrical socket to receive the first set of electrically conductive prongs, and a second set of electrical prongs electrically coupled to the electrical socket and arranged according to a second configuration different from the first configuration such that the adapter can be plugged directly into an electrical wall outlet, wherein the first device further comprises a movable element, wherein the first and second devices are electrically connectable to one another so that, when the first electrical connector is connected to the second electrical connector, the first surface of the first device contacts the second surface of the second device, said system characterized in that: the first surface is contoured to form two or more recesses (118a; 118b), each of which has a lip (120a, 120b), wherein a first of the recesses is on one side of the first set of electrically conductive prongs and a second of the recesses is on the other side of the first set of electrically conductive prongs; wherein the second surface is contoured to define two or more gripping elements (128a; 128b) each of which fits into one of the recesses (118a; 118b) grip one of the lips (120a, 120b) when the first and second electrical connectors are connected together; wherein each gripping element (128a; 128b) has a far end that is bent to fit behind and grip an associated one of the lips (120a; 120b) when electrically conductive prongs of the first device are plugged into the electrical socket of the second device, and wherein said movable element can be positioned such that when the two or more gripping elements (128a; 128b) are in the two or more recesses and gripping the two or more lips (120a, 120b) the movable element physically obstructs the gripping elements (128a; 128b) being moved out of the recesses or away from the lips (120a, 120b) the first surface is contoured to form two or more recesses (118a; 118b), each of which has a lip (120a, 120b), wherein a first of the recesses is on one side of the first set of electrically conductive prongs and a second of the recesses is on the other side of the first set of electrically conductive prongs; wherein the second surface is contoured to define two or more gripping elements (128a; 128b) each of which fits into one of the recesses (118a; 118b) grip one of the lips (120a, 120b) when the first and second electrical connectors are connected together; wherein each gripping element (128a; 128b) has a far end that is bent to fit behind and grip an associated one of the lips (120a; 120b) when electrically conductive prongs of the first device are plugged into the electrical socket of the second device, and wherein said movable element can be positioned such that when the two or more gripping elements (128a; 128b) are in the two or more recesses and gripping the two or more lips (120a, 120b) the movable element physically obstructs the gripping elements (128a; 128b) being moved out of the recesses or away from the lips (120a, 120b) wherein the second surface is contoured to define two or more gripping elements (128a; 128b) each of which fits into one of the recesses (118a; 118b) grip one of the lips (120a, 120b) when the first and second electrical connectors are connected together; wherein each gripping element (128a; 128b) has a far end that is bent to fit behind and grip an associated one of the lips (120a; 120b) when electrically conductive prongs of the first device are plugged into the electrical socket of the second device, and wherein said movable element can be positioned such that when the two or more gripping elements (128a; 128b) are in the two or more recesses and gripping the two or more lips (120a, 120b) the movable element physically obstructs the gripping elements (128a; 128b) being moved out of the recesses or away from the lips (120a, 120b)