Can I use a 90w adapter on a 65w laptop?

As a golden rule chargers "watt ac" can come down but it cannot power up.
Therefore you can use a 90 watt ac laptop charger for your 65 watt laptop. Under normal circumstances it will charge it quicker. However, you cannot use a 19 volt adapter on a 18.5 volt laptop - this may have dire consequences for your laptop.
If your laptop requires 240 watts of power (ie. a gaming laptop) then you will not be able to charge your laptop with a 90 watt charger.