Using the cigarette sockets for high powered devices?

[shift_deez]

Your mini fridge was probably blowing fuses because of the surge required to kick start the motor. Fridges need a power surge to start their motors and typical surge rating is 3 times that of regular voltage being drawn while running. So that could blow your fuse if that surge rating is well above that of the cig lighter's.
Laptops on the other hand don't use any surge because they don't have a motor to kick start. Whatever rating your laptop needs is what it will draw no matter how much processor intensive work you're doing. Only thing that will happen is that it will need to constantly pull power to keep topping off the laptop, but that's not a voltage or amperage increase. Just don't run that processor intensive app for long while plugged in and the engine not running otherwise it will deplete your battery quickly. That can lead to reduced battery life.

Enjoy your trip, u got nothing to worry about.