Wattage · The phone standard
20W adapters: 9V at 2.22 amps, and the whole iPhone story.
20W is the number Apple settled on for the iPhone and the number the rest of the industry treats as the floor. Two rails, one port, and enough power to bring a phone to roughly half charge in about half an hour.
The two rails that define it
Apple's 20W USB-C Power Adapter (A2305) publishes 5V/3A and 9V/2.22A. Third-party 20W bricks usually add a 12V/1.67A profile as well. The phone requests 9V the moment it is below roughly 80% state of charge and cool enough to accept it; above that it falls back to the 5V rail and tapers. That taper — not the adapter — is why the last 20% always takes longer than the first 50%.
Apple's published claim for every iPhone since the 8 is up to 50% in around 30 minutes from a 20W or larger adapter. Larger adapters do not beat that meaningfully on a standard iPhone, because the phone itself caps near 20W. On the Pro and Max models the peak drifts into the mid-20s, which is the argument for 30W.
Device map
| Device | Behaviour on 20W |
|---|---|
| iPhone 15 / 16 / 17 (standard) | Full fast-charge speed — this is the design target |
| iPhone Pro / Pro Max | Fast, but a couple of watts short of peak |
| iPad 10.9″ / iPad mini | Full speed; these ship with a 20W brick |
| Galaxy S-series (base) | Charges, but misses Super Fast Charging — that needs 25W |
| AirPods, Apple Watch, Kindle | Full speed; the device draws far less than 20W |
| iPad Pro 11″/13″ | Charges slowly — it wants around 30W |
| MacBook Air, Nintendo Switch | Not enough. Air wants 30W+, Switch needs 39W at 15V |
Picks at this wattage
- 20W
Apple 20W USB-C Power Adapter (A2305)
The reference. Published rails, Apple's own certification, and the exact part every iPhone box specified for years.
- Output
- 5V/3A, 9V/2.22A
- Port
- 1× USB-C
- Input
- 100–240V
- 20W
Anker Nano 20W-class GaN cube
Class pick for size. GaN switching lets a 20W brick shrink well below the Apple cube's footprint, usually with a folding plug.
- Output
- 20W PD
- Port
- 1× USB-C
- Body
- GaN
- 2-port
20W dual-port A+C charger
Class pick for a nightstand shared by a phone and a legacy accessory. Nearly all of these share the 20W total, so expect a split when both ports are busy.
- Output
- 20W total
- Ports
- 1× C, 1× A
- Check
- Shared total
When to size up, when it is overkill
20W is overkill for earbuds, watches and e-readers — those are 5W to 12W devices and gain nothing. It is one step above 18W, which is close enough that replacing a working 18W brick is not worth the money. Size up to 25W for a Galaxy, or 30W the moment an iPad Pro, a MacBook Air or a second device is involved — that step also adds a 15V and a 20V rail. The 20W vs 30W comparison puts numbers on it, and what wattage do I need maps every other device class.
FAQ
Is a 20W charger enough for an iPhone?
Yes. Standard iPhones peak at roughly 20W, so this is the design target rather than a compromise. Pro models can pull a few watts more, where a 30W adapter helps slightly.
Does a 20W adapter charge an iPad?
It fully fast-charges the standard iPad and iPad mini, which ship with a 20W brick. An iPad Pro wants closer to 30W and will charge noticeably slower on 20W.
Can a 20W charger damage my battery?
No. The phone requests each voltage rail itself and stops asking for 9V as it fills. Heat, not wattage, is what ages a cell, and a 20W charge on a modern phone is thermally mild.