Looks like both the X and 8 support fast charging (50% in 30 min) but they require a fast charger that's not included in the box. They tested them with Apple USB-C chargers.
"Testing conducted by Apple in August 2017 using preproduction iPhone 8, iPhone 8 Plus, and iPhone X units and software and accessory Apple USB-C Power Adapters (29W Model A1540, 61W Model A1718, 87W Model A1719). Fast-charge testing conducted with drained iPhone units. Charge time varies with environmental factors; actual results will vary."
https://www.apple.com/iphone/compare/
Should be able to use third party ones like this Anker too: https://www.amazon.com/dp/B06Y427WT7/?tag=neogaf0e-20
"Testing conducted by Apple in August 2017 using preproduction iPhone 8, iPhone 8 Plus, and iPhone X units and software and accessory Apple USB-C Power Adapters (29W Model A1540, 61W Model A1718, 87W Model A1719). Fast-charge testing conducted with drained iPhone units. Charge time varies with environmental factors; actual results will vary."
https://www.apple.com/iphone/compare/
Should be able to use third party ones like this Anker too: https://www.amazon.com/dp/B06Y427WT7/?tag=neogaf0e-20