Google reached out to Engadget this morning to confirm. "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," wrote a Google spokesperson. "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." The team also changed the wording and reopened the original case in the issue tracker.