The name says it all - cigar lighter. It was never designed electrically or mechanically to power external devices although (sadly) adopted widely by the auto accessory world for such. The worst aspect is the spring loaded centre contact on the plug which simply touches a surface within the socket. The tiniest amount of corrosion or burning on this surface compromises consistent current flow. The outer ground connection is not much better.
The Hella/DIN type offer captive centre contact as well as higher current rating.
