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The 18W USB-C Power Adapter that came with the latest Google Pixel 2 and Google Pixel 2 XL phones supports the same power profiles over USB Power Delivery technology as the Google Pixel's own charger. With that, we decide to see if the newer Google charger is also similarly backward  compatible when connected with the original Google Pixel over USB Power Delivery.

Using GRL-USB-PD-A1 test analyzer from Granite River Labs, we can clearly see what is communicated between the Pixel 2 18W USB-C Power Adapter and the Google Pixel with its battery fully drained. As expected, the Google charger first offers 15 watts (5 volts @ 3 amps) and 18 watts (9 volts @ 2 amps) in a repeated manner to initiate USB Power Delivery negotiation.

It takes a hard reset for the Pixel 2 18W USB-C Power Adapter to again advertise the same initial source capabilities.

Here we can see the Google Pixel goes ahead to request the highest 18 watts (9 volts @ 2 amps) power to charge at the maximum rate which the charger accepts.

Through the power graphs below, we are also able to see how long it takes for the Pixel 2 18W USB-C Power Adapter to charge the Google Pixel. We notice around 2 hours is needed to fill the battery up to almost full upon connecting the charger to the phone starting from zero battery level. 

We can see in the first hour of charging, upon initial power request, the Google Pixel starts pulling current in between 1.5-1.7 amps at starting voltage of about 9.1 volts, while the phone is off at 0% battery. As the voltage level keeps to around 9.1 volts, the current changes as seen being pulled by the phone throughout charging. After 3 minutes when the phone is turned on, it pulls lower current to about 0.7-0.9 amps band when reaching the first hour.

In the next remaining hour, the current further decreases to below .5 amps when the battery is near full. When the phone is turned on, we can see a lot more active current fluctuation.

At most the Google Pixel draws about 14.6 watts (9.1 volts @ 1.6 amps) during initial stage where it charges the fastest with the Pixel 2's 18W USB-C Power Adapter. When compared to how the Pixel charged with its own 18W charger, while the power drawn is quite similar, the entire charging duration is much shorter using the Pixel 2's charger given the smaller battery size of the Google Pixel compared to the Google Pixel 2 XL.