1, in fact, the spring clip of the plugboard is not a straight plate, but there is a small bulge at the tail, the charging head itself is very thin, even if there is a bulge, it may not be able to clamp, and after the small hole, it can be firmly fixed on the plugboard and socket. Make the plug not easy to fall off.
2, of course, now many new versions of the charging head material is more sufficient, thicker, making the metal plate in the connector metal deformation increased, to enhance the effect of friction.
3, and the three-head plug itself has the unique stability of the triangle, so it is not so easy to fall off, naturally rarely see the plug above the hole.