When replacing your laptop adapter, you should always choose a adapter with the same voltage as your original.It should always be less than or equal to Output voltage*(your old laptop adapter).

Never buy a charger whose output voltage is more than what is accepted by your laptop. It might damage the internal circuitry.

Always make sure that the voltage supplied by the power adapter matches the input voltage requirement of the laptop. It should never be more than that. The current rating, on the other hand, should always be equal to or more than what your laptop accepts.