Previously, I noted that the new iPhone 8/8 Plus (our review here) and iPhone X are fast charge-capable, but you’ll need one of Apple’s USB-C power adapters. I also assumed that this is made possible because the new iPhones support USB Power Delivery.
Well, I just spent some time with the smaller iPhone 8, and indeed, it supports USB Power Delivery. More specifically, it supports the 9V and 15V voltage levels. This is what allows it to work with the Apple 29W USB-C adapter, which can do 14.5V @ 3A; and the Apple 61W and 87W USB-C adapters, both of which offer a 9V @ 3A power rule in addition to their respective 20V voltage level.
Interestingly enough, while the iPhone 8 supports different voltages, I never saw the current anywhere near 3A. In fact, power draw typically hovered around 11.6W, and that’s regardless of which Apple USB-C adapter I was using. (I also tried a Xiaomi and an Anker USB PD-capable chargers and they yielded similar results.)
And here’s the thing: this charging rate has been doable for a while now via another method - Apple’s own 10W and 12W USB power adapters that come with most iPads. I did some testing with both on the iPhone 8, and I measured a 10.2W draw from the former and 10.6W from the latter. Yes, the USB-C PD-capable adapters have a higher peak, but not by much.
In case you’re wondering, yes, I also tried charging a fully depleted iPhone 8 with the Apple 29W USB-C and 12W USB power adapters; and on both occasions, the phone went from 0% to 52% in 30 minutes.
In short, if you’ve an iPhone 8 and want to top up its charge quickly, but the S$68 Apple 29W USB-C power adapter is giving you pause, you can consider the S$28 Apple 12W USB power adapter. If you’ve an iPad, you may already have it. By extension, any third-party adapters and power banks that support Apple’s 2.1A and 2.4A charging schemes should rapid-charge the iPhone 8 just as well.
And oh, Apple, you should really just bundle the 12W adapter instead of the also-S$28 5W USB adapter with your iPhones.
For what it’s worth, I didn't have time to plot out the whole charging curve, so there’s always the possibility that the USB-C adapters are able to sustain the power peak for a longer period, and thus able to charge the iPhone 8 from 0% to 100% much faster than the 10W and 12W adapters.
Also, I didn't get to test the iPhone 8 Plus in detail. It’s entirely possible that the USB-C adapters make more sense with the bigger phone. Since the Plus has a bigger battery, I expect the USB-C adapters to supply more power so that the phone can hit the same “up to 50% charge in 30 minutes” claim.
Update: I measured around 15W (a couple watts more with screen on) when an iPhone 8 Plus, with around 30-ish percent charge, was connected to Apple's USB-C power adapters. So yes, the Plus model will get charged faster on a compatible USB-C/PD charger than the regular 10W or 12W iPad adapter.
Overall, I see this support for USB PD on the new iPhones as a great first step to enable even faster charging down the road. Apple’s 2.1/2.4A charging identification schemes have always been its own thing, and while they work well for its own products thus far, they also limit what Apple can do for future products. (Keep on increasing current is an untenable method.) With USB-C and USB Power Delivery, Apple now has an easier time when, say, designing a future iPhone that can be charged up to 50% in 15 minutes.
Update, Sep 22, 11:30 AM: Added some iPhone 8 Plus charging stats.
I write. I also fix things.