https://www.theverge.com/circuitbreaker/2018/8/14/17689040/google-pixel-fast-charge-android-pie-fix-coming-soon

Google is currently testing a software fix that will fully restore the fast-charge functionality of its 2016 Pixel smartphones after users reported slower charging speeds following the recent upgrade to Android 9 Pie. Some third-party charging plugs no longer rapidly charge the Pixel XL in the same way that they did prior to Pie’s release; Google says its own bundled charger (and others certified for USB Power Delivery) should still be delivering rapid charging. Assuming the update is verified and tested successfully, it will be available “in the coming weeks.”

“We’re aware of an issue where non-Power Delivery (PD) USB-C chargers no longer rapidly charge the 2016 Pixel and Pixel XL after the upgrade to Android 9 Pie,” a Google spokesperson told The Verge by email. “The 18W rapid charger included in-box is a PD charger and does not exhibit this behavior. We are verifying a fix for non-PD USB-C chargers and will roll it out in the coming weeks.”