Both Dell and HP use what is known in the industry as Smart Tip technology on their laptop chargers. Therefore if you have a laptop rated at 45W you can safely use a 45W, 65W, 90W, 120W or higher rated charger. The laptop will only draw the power required at the time.
What size charger does a Dell Inspiron use?
19.5V 3.34A 65W AC Power Adapter Charger for Dell Inspiron 15-3000 15-5000 15-7000 11-3000 13-5000 13-7000 17-5000 XPS 13 Series 5559 5558 5755 5758 P20T002 with Size 4.5mm 3.0mm.
What happens if you use a 65W charger for a 45W laptop?
As long as it is the same voltage and connector type you can use a higher watt adapter. It will charge the battery a bit faster but other than and the size of the brick you will see no difference. The laptop will only draw the current it needs while running.