Shortly after the original Pixel XL was updated to Android 8.1, many users took to the depths of the internet to complain about a new charging bug that came with it. Google addressed this issue in late March, saying that "a fix will be rolling out in the coming weeks." With the May 2018 security patch, that fix is finally here.
As noted in the Pixel/Nexus Security Bulletin, one of the functional patches included (reference number A-72851087) has an improvement to "adjust Pixel XL charging behavior."
It's great to see that a fix has arrived, but what went wrong in the first place?
Following the release of 8.1 Oreo for the original Pixel series, Pixel XL owners began reporting that they were unable to charge their phone with the included cable and AC adapter. After being plugged in, the Pixel XL would begin charging, stop, resume charging, stop again, and repeat this process over and over until it was full.
As noted by Nathan K in the Pixel User Community who dived deeper into the bug –
The OEM Google 18w charger (and OEM cable) is being overloaded by the Pixel 1 XL. The charger is only capable of 9v/2a, but the Pixel 1 XL (at least, mine on 8.1.0 OPM1) is drawing up to 2.8a+. This causes the charger to recognize an overcurrent fault condition, shut down, and reboot.
This issue should be resolved after updating your Pixel XL to the May patch, so be sure to drop a comment below once you're running the new update to let us know how it's running.