Samsung no longer ships a charger in the box with its flagship phones and even most of its mid-range devices. You're meant to use one that you already have or the company will happily sell you one separately.
As you'd probably expect, the official chargers from Samsung cost quite a bit of money, more than what you'd normally pay for a third-party charger, but it's always best to use an official accessory so when you can buy one at a discount, it's a good opportunity to pick one up.
If you buy the official Samsung 25W charger from Amazon today, you can save 26% on the regular price and get it for $25.98 only. This price is only available for a limited time so you best hurry!