Determining input voltage range
First you should determine the range of voltage that is required by your laptop. The usual voltage range supplied by common cars is 12v.So you should look up for the car adapter that best matches the voltage range ranging from 10 to 24 volts. It is because the more the range of the car adapter the more is the chance of better adaptability to fluctuation of voltage when car is in running condition. If you consider low voltage it may cause the laptop to shut down and may harm its battery as well.
Determine the output power level
The out put power level should also be considered .It can be determined with the help of instructions given on the laptop. The output voltage depends upon the input voltage. Such consideration can be helpful in safe usage of car adapter and laptop may function better with better input and output voltage level.
The fuse design
You should carefully take into consideration the size and shape of the fuse. In order to get the exact fuse size to be put in can get a better result in laptop functioning. The fuse size is important because if the fuse is not best fit to the socket it may cause the loosening of the socket and cause the charge to get wasted and may heat up the socket joint causing serious damage to the laptop.
Input pins should also be noticed while purchasing the car adapter as their may be certain variation regarding the pins present on the cord .Choose the one which is exact fit to your laptop.
In addition to all these technical issues there are certain minor but important issues that are also important to consider to take into consideration. Such as the length of the wire needed for the charger, the weight of the adapter etc. In order to make a better choice you should take into consider al these important issues as these can play an important role in purchasing a better car adapter for your laptop and the better functioning depends on what to choose as a car adapter..