Since the GoPro Supercharger (click here for Amazon pricing) supports USB Power Delivery charging, you can also use it to quickly charge your LG G6 phone as an alternative to its own charger.
The GoPro Supercharger offers the following USB Power Delivery based charging profiles: 15 watts (5 volts @ 3 amps), 16.5 watts (5.5 volts @ 3 amps), and 20 watts (12 volts @ 1.67 amps). The LG G6 follows up to request 16.5 watts (5.5 volts @ 3 amps) which is accepted by the charger.
On a fully drained battery, the charging current level can be seen stepping up to reach 3 amps at 5.5 volts (16.5 watts). We can confirm that the LG G6 is able to charge well with the GoPro Supercharger using USB Power Delivery.