Wireless charging is normally slow compared to charging with a cable, but recently some OEMs have enabled faster wireless charging in their devices. Samsung is well-known for this and the Pixel 3 and Pixel 3 XL will actually charge at 10W if you're using the Pixel Stand and other certified devices from the Made for Google program (Belkin announced its 10W charger late last year). However, if you're using a non-certified Qi wireless charger then you will typically get about 750mA charging current by default.
This is done for a number of reasons (such as heat generation), but some modders have figured out a way to increase the wireless charging speed of the Pixel 3. XDA Senior Member k0rner published this mod over the weekend and said he was able to increase the wireless charging current up as high as 1,290mA. This is done by changing the value of /sys/class/power_supply/wireless/voltage_max to 9000000 (from its default 5000000).
The change needs to be made while the device is wirelessly charging because once the charging session is over, it will reset to its default state. However, this setting can be made permanent by using the Advanced Charging Control Magisk Module (as long as you go in and change the code to add onPlugged=./wireless/voltage_max:9000000).
Warning: Any modification that messes with charging can be risky. You should always use high-quality chargers for your devices.