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macrumors regular
Original poster
Mar 5, 2017
We don't know yet how Apple will implement type-C on the iPhone 15 and later. Ideally, it'll be something similar to the Mac, iPad, etc. that mostly charge at peak output with any high-enough wattage USB PD charger. Now, Apple may find certain ways to get around this (hopefully not).

To be prepared on whatever eventuality, I thought let's make a dedicated thread. This will get a little technical, but only to the point of helping you find which chargers support which devices.

It's technical enough to understand compatibility as listed on the USB PD charger box or Amazon / B&H Photo / Walmart e-tailer description, but not more than that!
  1. USB-PD = USB Power Delivery, the overarching specification on USB devices charge, including type-C. All newer versions of USB PD require USB-C and don't work with USB-A or USB-B. You need "PD" clearly written somewhere on your charger (Apple even writes "PD", as averse as they are to regulatory labels).
  2. USB-IF = USB Implementers Forum, the industry body that designs & certifies everything USB (ports, data, power), from little old USB 1.1 to USB4. Apple is a long-term Board Member of USB-IF.
The USB-IF has set standards on how USB PD should work, though Apple has ignored the USB-IF before and it might do it again. No matter, the key lesson here: compatibility is made / broken based on voltages. The device and the charger (and sometimes the cable, see endnote) need to have the same voltage available.

This is just like travelling internationally: 120V AC here in the US, 240V AC in the UK. Your charger needs to explicitly confirm its compatible voltages. That's AC. USB-PD does a similar compatibility scheme, just for DC. Most device chargers do multi-voltage input (120V vs 240V AC, from the wall) and multi-voltage output (USB PD's 5V vs 48V DC, to your device).

USB-PD is rationally designed for safety, power output, and compatibility. USB-IF does certify 1) cables and 2) chargers, which can greatly improve compatibility and safety. But USB-IF certification is not common: think retailers with legal liability (Best Buy, other big-box chains, industrial, commercial) if you want to find a USB-IF certified charger.

Briefly, voltages (V) * amps (A) = watts (W). 5 Volts x 3 Amps = 15 Watts. Each voltage must have a maximum amperage listed (so 5V below works at 5V * 0A min → any amperage between 0A to 3A → 5V * 3A max.


How USB-IF has designed USB-PD chargers (2016 & onwards)

All USB-PD voltages are 1) incrementally added and 2) work from 0 amps to 3A (max). Your charger will decide which voltages it supports and to what maximum amperage it'll go on each voltage. You can go beyond 3A (to 5A, but 5A is a hard limit for all of USB-PD; more than 3A requires a special e-marked USB-C cable and is not relevant for phones).

Incrementally added: each charger must start with 5V and offer the complete 3A before it can offer 9V. Then it must max out 9V and then it can max out 15V, and then it can max out 20V. You can't have a USB-PD charger that is only 15V or only 9V. It must be 5V or 5V+9V or 5V+9V+15V or 5V+9V+15V+20V. Each voltage is incremental and you cannot add the next voltage until you've offered the full 3A on the preceding voltage (e.g., gotta have 5Vx3A to allow 9Vx2A; you can't ship 5Vx1A and then suddenly add 9Vx2A--you need to offer the full 3A capacity of 5V first).

So how do you know what voltages are supported? Read the label: it will be there. But sometimes, they don't show you the little label. A shorthand is the wattage: that will roughly tell you the voltages, if we're looking at any reputable brand. Wonder why why we frequently see "15W" and "27W" and "45W" USB-PD chargers? These numbers indicate they've maxed out that voltage and offering even 1W more (16W or 28W or 46W) would require a brand-new voltage, which often means re-designing the charger.

5Vx3A = 15W max allowed on 5V
9Vx3A = 27W max allowed on 9V
15Vx3A = 45W max allowed on 15V
20Vx3A = 60W max allowed on 20V


15W and less chargers = 5V, usually
27W and less chargers = 5V+9V, usually
45W and less chargers = 5V+9V+15V, usually
60W and less chargers = 5V+9V+15V+20V, usually
60W to 100W chargers = 5V+9V+15V+20V, usually, with the 20V @ 5A
100W to 240W chargers = 5V+9V+15V+20V, and also 28V / 36V / 48V

Work from 0A to 3A: each charger can do each voltage at 0A → xA in a continuous range. 0.00A, 0.45A, 2.452A, etc. to a maximum of 3A. But each charger can stop anywhere between 0A to 3A, so 5Vx3A + 9Vx2A is still good. That charger just didn't max out the 9V capacity, which is fine (but it means this charger cannot support 15V at all, even though 15Vx1A = 15W and that's less than 9V).

  • USB-PD Rev 2.0, Version 1.2 (like ~95% of all USB-C chargers today)
    • 5V @ 0A to 3A
    • 9V @ 0A to 3A
    • 15V @ 0A to 3A
    • 20V @ 0A to 3A (to 5A with e-marked cables)
  • USB-PD Rev 3.0 (adds the optional PPS, Programmable Power Supply, Protocol)
    • 5V @ 0A to 3A
    • 9V @ 0A to 3A
    • 15V @ 0A to 3A
    • 20V @ 0A to 3A (to 5A with e-marked cables)
    • Optional: PPS 3.3V to 21V (continuously; not just 15V or 20V, but 15.00V, 15.02V ... → ... 19.96V, 20.00V)
  • USB-PD Rev 3.1 (adds the optional EPR, Extended Power Range, Protocol)
    • 5V @ 0A to 3A
    • 9V @ 0A to 3A
    • 15V @ 0A to 3A
    • 20V @ 0A to 3A (to 5A with e-marked cables)
    • Optional: PPS 3.3V to 21V (continuously; not just 15V or 20V, but 15.00V, 15.02V ... → ... 19.96V, 20.00V)
    • Optional: EPR 28V+36V+48V (more fixed voltages for ultra-high-power type-C charging)
Instances where Apple ignored USB-IF standards
(because when does Apple not do their own thing?)
  1. Apple's 30W USB-C Charger
    1. This charger adds a 20V @ 1.5A, but it did not max out the 15V @ 3A. It only offers 15V @ 2A. Not a big sin, as it's actually more compatible, but still bucks the rules.
  2. Apple's 29W USB-C charger
    1. This charger offered 5V and 15V, skipping 9V. Definitely not good. This weird 29W charger was discontinued because many Apple devices, most prominently MagSafe, required 9V and Apple's own charger did not include 9V (!).

Cable endnote:

USB-PD cabling is relatively universal for phones (not all phones use USB-PD, however): all cables are meant to support all voltages and amperages for charging 60W and below (thus 5V to 20V). Only two cable safety certifications are relevant and only to MacBook owners: 60W+ charging and 100W+ charging, both which require additional safety hardware in the cables (e-marking and EPR marking, respectively).

But those only concern 60W+ charging, so likely irrelevant to any foreseeable iPhone launch.

Now, if you own a high-powered 60W+ charging MacBook, then you could consider buying only these cables so you don't have two species of cable floating around: one that fast charges the MacBook and one that doesn't.

Multi-USB-C port charger endnote:

Buyer beware, these can be tricky. Most USB-C chargers 1) do not offer equivalent power on all USB-C ports and 2) can idiosyncratically (seemingly randomly) split USB-C power. So a 100W charger cannot charge two devices at 100W; it'll split the 100W. But it's not always a 50:50 split and it might not even total back to 100W. Maybe the first port is 65W and the second port is 35W. Or 45W and 18W (yes, you 'lose' the other 37W; you need to unplug something first).

That is because internally, multiple USB-C charging ports can be combined / rely on a single charging circuit (this is very normal for all chargers, so it's not unique to type-C!). So they split the volts and amps however the manufacturer designed it, depending on 1) how many devices are connected and 2) which USB-C ports have which devices This is also why sometimes when plugging in multiple USB-C devices to these multi-USB-C port chargers, each will briefly stop charging as they re-negotiate with the charger on a new power profile.

Usually, the 'first' port is the fastest / highest priority port and should be used for your most power-hungry USB-C devices. This is a genuine efficiency measure. You do not want to know the price, nor size nor weight, of a fully-versatile 100W on every port at all times sort of device.

The better multi-port charges will 1) tell you how they split it and 2) it'll be a sane split, where you aren't losing most of the charger's alleged total watt output.
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