Yes and no. So there are really 4 different levels of charging supported by iPhone 8, 8 Plus, and X. The included 5W power adapter in the box, up to 7.5W with wireless charging, up to 12W with an iPad or larger charger, and then the fastest charging using a USB-C adapter. The cable used also affects the charge rate. A lightning to usb cable that is plugged into and USB to USB-C adapter, plugged into a USB-C power adapter as you have described will only charge at up to 12W because of the actual cable. If you want to achieve the fastest possible charging speed you'll have to purchase a USB-C to lightning cable.