The Nintendo Switch AC Adapter was made for the Nintendo Switch to keep the Switch charged using USB Power Delivery over USB Type-C. Because it uses the USB Power Delivery standard, the Nintendo Switch AC Adapter should also be able to charge other USB Type-C and Power Delivery enabled devices like the Google Pixel phone.
Looking at the USB Power Delivery negotiations between the Nintendo Switch AC Adapter and Google Pixel, the charger can be seen to constantly advertise its source capabilities of 7.5 watts (5 volts @ 1.5 amps) and 39 watts (15 volts @ 2.6 amps).
After a hard reset is done, the Google Pixel does requests power but not one of the PDO's supported by the charger, which is then rejected.
Several hard resets later, the Google Pixel finally requests to pull 7.5 watts (5 volts @ 1.5 amps) which the Nintendo Switch AC Adapter accepts.
While the Google Pixel is being charged with its battery at around 40% full, we can confirm that the phone charges at 7.5 watts (5 volts @ 1.5 amps) with the Nintendo Switch AC Adapter.
The Nintendo Switch AC Adapter is able to work with the Google Pixel although the initial USB Power Delivery negotiation is far from being clean.