Despite rumors suggesting Apple's 2018 iPhones might ship with an 18W adapter and a Lightning to USB-C cable to enable fast charging right out of the box, that didn't end up being the case.
The iPhone XS, XS Max, and iPhone XR ship with the same standard 5W Power Adapter that's traditionally included with iPhone models. The three devices also include a standard Lightning to USB-A cable, despite the fact that Apple's current Mac lineup has been transitioned to USB-C.
Those who want to use fast charging on the new 2018 iPhones will continue to need to purchase an 18W+ power adapter and a USB-C to Lightning cable.
There are plenty of third-party 18W+ power adapters on the market (or you can get a 30W MacBook charger from Apple for $49), but Apple sells the only certified Lightning to USB-C cable at this time. Apple is planning to let other manufacturers make these cables, but third-party USB-C to Lightning cables aren't expected until next year.
With fast charging, iPhone models are able to charge to 50 percent battery life in a 30 minute time span. iPhone XS, iPhone XS Max, and iPhone XR all support fast charging.