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With USB Power Delivery, the Apple iPhone 8 can charge at a higher power using the Apple 29W USB-C Power Adapter than its own 5 watts based power adapter as recently reviewed. We also want to know how long it takes to power the iPhone from 0% battery to full charge with the same Apple charger which we demonstrate below.       

Once connected over the Apple USB-C to Lightning Cable, we can see using the GRL-USB-PD-A1 test software from Granite River Labs, the Apple 29W USB-C Power Adapter starts to communicate over USB Power Delivery by constantly advertising 12 watts (5 volts @ 2.4  amps) and 29.6 watts (14.8 volts @ 2 amps) power profiles.

As observed after a hard reset, the Apple 29W USB-C Power Adapter also declares the same 12 watts (5 volts @ 2.4  amps) and 29.6 watts (14.8 volts @ 2 amps) power capabilities.

The Apple iPhone 8 starts to request only 12 watts (5 volts @ 2.4 amps) from the Apple charger and gets accepted.

After establishing the initial 12 watts (5 volts @ 2.4 amps) power contract, both the iPhone and Apple charger can be seen to exchange  multiple Vendor Defined Messages such as Discover Identity, SVIDs, Discover and Enter Modes, and Unstructured VDM.

After the Vendor Defined Messages have completed only does the Apple iPhone 8 request the max 29.6 watts (14.8 volts @ 2 amps) to charge faster with the Apple 29W USB-C Power Adapter, which the charger also complies.

After plugging in the Apple iPhone 8 to the Apple 29W USB-C Power Adapter, starting with a fully depleted battery the iPhone takes about 185 minutes to fully charge.

We can see that it takes almost 40 seconds from initial plugin for the iPhone to finally start pulling current at 5 volts while switched off or in sleep mode. During the first 12 watts (5 volts @ 2.4 amps) request, there is a brief period that 2.8 amps is pulled but after which the current mostly stays around 2.4 amps at 5 volts. When the 29.6 watts (14.8 volts @ 2 amps) request takes place does the voltage level rise up to 14.8 volts but which point the current pulled is under 1 amps, while the iPhone is turned on and being used.

After the first 55 minutes the current even drops to zero for about 5 minutes before resuming to charge at 0.27 amps @ 14.8 volts.

In the next 61 minutes of charging, as the current is being pulled at about 0.8 amps, the voltage drops down to 5.2 volts. The current then steadily goes down to 0.1 amps with random spikes in between while the voltage remains at 5.2 volts. 

As charging is almost complete, the current eventually goes down to near 0 amps at 5.2 volts.

Throughout the entire power charging cycle, we see the current at most stays below 1 amps when the voltage level is at both 14.8 volts and later 5 volts. Still the power drawn is higher than the 5 watts provided by the iPhone's own charger to enable the Apple iPhone 8 to charge quickly in about 3 hours and 5 minutes with the Apple 29W USB-C Power Adapter using USB Power Delivery.