Nope the socket is the normal size, it is just a bit shallower than some of the other sockets so some accessories will fit very loosely or not make contact as they were designed for a longer socket.
For example, all of the dual-USB/12V socket adapters from Super Cheap Auto here do not fit my 500C, they're all too long to make proper contact. I randomly bought a Dolphin Essentials dual-USB/12V adapter for $4 from my local Woolies which fits perfectly.
There really ought to be a proper industry standard for 12V lighter sockets. Grrr...