Choosing a right charger isn't actually as hard as it seems - You only need to follow some guidelines.
The most important thing when choosing a charger, is to identify the plug size (in mm), voltage (V) and amperage (A). The new charger can be up to 2x more powerful than the original one. This means that if Your old charger is, let's say - 65W, then 90W charger is also suitable. It doesn't harm the computer.
More information about choosing a charger (in Estonian) - HERE