Despite its widespread adoption, the connector [Molex 4-pin power] does have problems. It is difficult to remove because it is held in place by friction instead of a latch, and some poorly constructed connectors may have one or more pins detach from the connector during mating or demating. There is also a tendency for the loosely inserted pins on the male connector to skew out of alignment. The female sockets can spread, making the connection imperfect and subject to arcing. Standard practice is to check for any sign of blackening or browning on the white plastic shell, which would indicate the need to replace the arcing connector. In extreme cases (as in vintage pinball machines which often use this style of connector), the whole connector can melt due to the heat from arcing.
So moral of the story... Use a proper extension cable, not an adapter.