Laptop Charger 65W or 90W

If the system has Intel video, 65W is fine.  If AMD or nVidia, 90W is required.  90W will work in place of 65 (but the reverse WILL NOT work).

Just fyi, it's completely fine to buy a higher wattage charger than you originally had.  Some laptops can actually charge faster when connected to a higher wattage adapter, but even if they can't, you won't cause any damage; the PC simply won't take advantage of the extra capacity if it can't use it.  The only downside to this strategy is that higher wattage chargers can be a bit more expensive and a bit larger.

You WILL however need to make sure that you buy a charger with the correct connector size.  Dell now has their older 7.4mm barrel size and their slim 4.5mm barrel size, and there are 65W and 90W chargers available with both connector types.

I haven't checked personally, but I believe ejn63's advice is correct about charger wattage.  But if you want to be sure, go to support.dell.com, enter your Service Tag, select System Configuration, and choose Original Configuration.  That will show you the spec of your system as it shipped from the factory, including the AC adapter wattage.

Can I use 90w charger instead of 65w on Dell Inspiron 5559 i7 6gen amd m335 gpu?

@vikkyshaikh  Yes, it's always completely fine to use higher wattage chargers as long as they're official Dell chargers.  The laptop will only draw the amount that it actually needs.  The charger won't "force" the system to accept more power than it can handle.  I have had a 130W Dell charger in my living room for years and I have used it with many Dell laptops designed for power levels ranging from 45-130W, and it has been completely fine with all of them.