This means you can get up to 50% power after 30 minutes on the cable, as 9to5Mac uncovered, if your battery is completely drained from the start.
However, there is a sizeable caveat to taking advantage of fast charging: Your phone needs to be connected via USB-C. Though wireless charging is one of the key features of the new iPhone models, it won't support fast charging.
Here's the kicker: Apple doesn't include the necessary accessories for fast charging - a USB-C to Lightning cable and a USB-C Power Adapter - in the box, so you'll need to purchase these separately, either from Apple or somewhere else.
A USB-C to Lightning Cable retails for $25 (£25 / AU$35) on Apple.com, while a USB-C Power Adapter can be purchased in one of three sizes for: 29W, 61W and 87W. The cost of the cheapest adapter (29W) is $49 (£49 / AU$69) from Apple.
While there's a price to pay for fast charging on top of the cost of your new iPhone, it's actually not too surprising this is the case considering Apple is utilizing USB Power Delivery charging spec, as The Verge points out.
It's a bit vexing to buy extra accessories when you've already forked over $999 / £999 / AU$1,579 for an iPhone X, but if you want to get your new iPhone up to serviceable battery life quickly, then fast charging is a convenient way to go.
Just be ready to pay for that convenience.