Nathan Park, a freelance hardware engineer, has carried out tests on the Google Pixel 2 XL, discovering an intentional bottleneck on the device that limits the power received by the phone from the 18W supplied by its stock charger to just 10.5W.
https://www.notebookcheck.net/Google-Pixel-2-XL-s-charging-measured-at-10-5W.262434.0.html