A recent update to Google's Android documentation attempts to discourage handset makers from using proprietary charging methods like Qualcomm's Quick Charge.
Instead, Google "strongly recommends" that, alongside the increasingly common Type-C standard, manufacturers adopt USB Power Delivery—which Google implemented in its recent Nexus and Pixel devices for fast charging.
"Type-C devices are STRONGLY RECOMMENDED to not support proprietary charging methods that modify Vbus voltage beyond default levels, or alter sink/source roles as such may result in interoperability issues with the chargers or devices that support the standard USB Power Delivery methods," the Android doc explains.
For now, this is voluntary, but "in future Android versions we might REQUIRE all type-C devices to support full interoperability with standard type-C chargers," according to the document.
This is not the first time Google has addressed this issue. Google engineer Benson Leung, a USB evangelist of sorts, first discussed his concerns in a late November 2015 blog post about whether Qualcomm QC and USB Type-C can coexist on the same connector. In a nutshell, he said, "Type-C Spec forbids it."
As Android Authority outlined earlier this year, the USB Type-C specification requires that a port's Vbus line sits between 4.45 and 5.25 volts. Qualcomm Quick Charge, however pushes that to 9 or 12 volts.
In April, Qualcomm said "Quick Charge is designed to be connector-independent. It can be implemented in a device that supports a variety of connectors, including USB Type-A, USB micro, USB Type-C, and others.
At least two flagship smartphones, the HTC 10 and LG G5, include Quick Charge and USB-C.