The Apple iPhone X conveniently supports USB Power Delivery fast charging technology over its Apple Lightning connector, allowing this newly released iPhone to get faster charging with other USB Power Delivery chargers such as the Apple 87W USB-C Power Adapter than the iPhone's given 5 watts based USB power adapter accessory. Here we try pairing the Apple iPhone X with the Apple 87W USB-C Power Adapter over USB Power Delivery while the iPhone is 67% charged.
Once we connect the Apple iPhone X with the Apple 87W USB-C Power Adapter using a Apple USB-C to Lightning Cable, we first observe VBUS going to 5V as it gets ready to charge non USB Power Delivery Lightning based devices. This is then followed by USB Power Delivery protocol transactions which initially show the Apple charger consistently declaring 12 watts (5 volts @ 2.4 amps) over the Granite River Labs GRL-USB-PD-A1 test software.
The Apple iPhone X doesn't seem to take advantage of the higher power offering to still settle on the same 12 watts (5 volts @ 2.4 amps) power contract with the Apple charger.
We then observe both the iPhone and charger further communicate over multiple Vendor Defined Messages such as Discover Identity, SVIDs, Discover and Enter Modes, and Unstructured VDM.
When initially plugged in at 67% battery and switched on, it takes almost 20 seconds for the Apple iPhone X to finally start trickle charging at around 5.1 volts. During a hard reset the iPhone stops charging for a while before it quickly resumes to trickle charge at 5.1 volts after the first 12 watts (5 volts @ 2.4 amps) request and over Vendor Defined Messages. As the voltage rises to 9 volts from the 27 watts (9 volts @ 3 amps) power contract, the current pulled increases from about 1 amps to 1.7 amps but goes back down to about 0.9 amps while still at 9 volts. The current again starts to fluctuate when near to 60 seconds, but stabilizes down to around 1 amps @ 9 volts after 70 seconds. The iPhone later goes back to rapidly pull current which eventually settles out to draw power at around 9 watts (9 volts @ 1 amps).
We only manage to see mostly 9 watts power being drawn although 15.3 watts was briefly pulled during the initial 9 volts charging. While it can't achieve the requested 27 watts, the Apple iPhone X is still able to charge faster using the Apple 87W USB-C Power Adapter rather than the slow 5 watts based charging through its own supplied power adapter.