https://www.theverge.com/circuitbreaker/2018/10/23/18016492/google-pixel-3-fast-wireless-charging-approved-chargers-restriction-qi

One of the more convenient additions to the Pixel 3 and Pixel 3 XL this year was support for wireless charging. Google embraced the new tech with a Pixel Stand accessory that can charge both new phones while providing easy access to Google Assistant and even acting as a photo frame.

But it turns out that there’s a catch: if you want to get the fastest wireless charging speeds out of your Pixel 3, you’ll need to own the Pixel Stand (or another, Google-licensed 10W wireless charger) to take advantage of those speeds. Otherwise — even if you’re using a third-party charger that can support faster wireless charging — you’re stuck at the 5W Qi spec that’s serves as the base Qi charging speed.