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The GoPro Supercharger is a USB Power Delivery enabled charger that is promoted by GoPro as a fast charging accessory to its GoPro HERO5 Black and GoPro HERO5 Session which uses a USB Type-C connector for charging.

Let's see how well the GoPro Supercharger charges the Google Pixel phone which also uses USB Power Delivery for charging.

Looking at the USB Power Delivery negotiations between the GoPro Supercharger and the Google Pixel, we can see that the GoPro Supercharger is constantly advertising its source capabilities of 15 watts (5.1 volts @ 3 amps), 16.5 watts (5.5 volts @ 3 amps), and 20 watts (12 volts @ 1.67 amps).

After a while, there are multiple attempted requests by the Google Pixel to charge from the GoPro Supercharger which get rejected. 

For some reason, after a while the GoPro Supercharger accepts the Google Pixel's request to pull 15 watts (5 volts @ 3 amps).  

While the GoPro Supercharger charges the Google Pixel with the phone's battery being fully depleted, we can see that the current charges from 2.6 amps to 2.9 amps during the first 26 minutes.  In the next 16 minutes, the current falls to 2.3 amps to 2.4 amps.  In the next 24 minutes, the current falls further to 1.4 amps to 1.5 amps.  As the phone battery gets closer to being full, the current steadily drops to .2 amps. 

The GoPro Supercharger can charge the Google Pixel using USB Power Delivery but the entire USB Power Delivery negotiation is far from being clean.