Cigarette Socket Overload?

Having read with interest the responses to Ron's query about 12 volt wiring, and having had an overload(?) problem ourselves, maybe those of you with expertise could also provide advice on our power/wiring question.

We like to travel quite simply in our Hilux 2.8 diesel and don't carry any heavy current-pulling appliances such as a fridge or power winch etc. (Yes I know, de-hyd tucker and no cold beers but it suits us well). However we do make good use of the standard cigarette-lighter socket to power and recharge small items such as GPS, rechargable torch and "Power-Pac" (12 Volt powersource / portable emergency jumpstarter). In order to be able to use several items at once, i.e. continue to run the GPS while charging the other items, we purchased a multi-socket adaptor for the cigarette-lighter socket. This seemed to work well until we found the plug in the lighter socket one day melted! Thankfully this appeared to be the extent of the damage. We are naturally quite wary about hooking up a similar setup again.

Our question is why this might have occurred, given that both the lighter and the adaptor itself had fuses which one would expect might have blown before the potentially dangerous situation of meltdown began. If the fault is simply a faulty adaptor or incorrect fuses, then replacement is the easy solution, but might we could we need to look more deeply at the wiring in the truck itself? Any suggestions?