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If your Samsung Galaxy S8 is running low on battery when there's no AC power output lying around, you can link it to another Android phone like the  Google Pixel for a quick recharge. The Google Pixel is capable of charging in both directions meaning it can act as a power bank and charging other phones as well as being able to be charged itself (which is also similar to the Samsung Galaxy S8).

With both phones supporting USB Power Delivery fast charging technology, we take a closer look at how well the Google Pixel supplies power to the Samsung Galaxy S8 using USB Power Delivery over USB Type-C. Just be aware that this will also force the Google Pixel to consume its own battery power if standalone without AC input.

Using a USB Type-C to Type-C cable, we directly connect the Google Pixel on a 30% charged battery with the Samsung Galaxy S8 which has only 2% battery charge left. Under the Pixel's USB settings, we then turn on the option to enable USB charging.

When looking at the GRL-USB-PD-A1 analyzer by Granite River Labs, Vendor Defined Messages are first seen to occur to adjust voltage and current. The Google Pixel then follows up to promote its sole USB Power Delivery profile of 7.5 watts (5 volts @ 1.5 amps).

We then observe the Samsung Galaxy S8 initially requests this 7.5 watts from the Google Pixel and gets accepted.

After exchanging Discover Identity with the Samsung phone, the Google Pixel goes on to showcase a repeated display of a different 4.5 watts (5 volts @ .9 amps) power profile.

After some time, we see that the Samsung Galaxy S8 also wants to use this 4.5W option which is agreed upon by the Pixel phone. The negotiation then continues with the Google Pixel initiating several Vendor Defined Messages such as Discover Identity and SVIDs with the  Samsung Galaxy S8.

However, we only observe charging over the first 13 minutes, after which the Google Pixel's battery has fully drained.

When initially connected to the 30% charged Pixel, the Samsung Galaxy S8 starts pulling around 5 watts (5 volts @ 1 amps) at first power request  when the phone is on at 2% battery. While the phone is in sleep mode, it pulls higher current up to about 1.5 amps at 4.8 volts. As it gets close to 13 minutes of charging over 2nd power request and Vendor Defined Messages, the phone suddenly stops pulling current to terminate charging with the  Google Pixel.

We can see that the Samsung Galaxy S8 has completely used up the Google Pixel's battery after about 13 minutes of charging. The Samsung Galaxy S8 is still able to get around 7.2 watts (4.8 volts @ 1.5 amps) during initial charging with the Pixel which is close to the power achieved when using the Samsung Adaptive Fast Charging Charger to charge the Samsung phone as seen in this review. The Google Pixel can serve as a quick charging method for the Samsung Galaxy S8 but just make sure the Pixel has sufficient battery charge to cater for this situation.