Wattage · Dynamic power & 20+20 dual
40W adapters: two very different bricks share the number.
Buy 40W and you get one of two completely different products: Apple's Dynamic Power Adapter, which can surge past its rating on a single port, or a conventional dual-port unit that is really 20W plus 20W. They suit opposite users.
The two 40Ws
| Apple 40W Dynamic Power Adapter | Generic 40W dual-port | |
|---|---|---|
| Ports | 2× USB-C | Usually 2× USB-C, sometimes C+A |
| Sustained rating | 40W total | 40W total |
| Single-port behaviour | Dynamic boost above the 40W rating for short bursts | Flat — one port takes 20W or the full 40W depending on model |
| Two-device behaviour | Splits, prioritising the higher-draw port | Typically a fixed 20W + 20W split |
| Best for | Fastest possible iPhone charging plus a second device | Two phones, or a phone and a tablet |
What "dynamic" actually means
Apple's adapter is rated 40W for continuous delivery but is engineered to supply more than that briefly when a single device asks for it — the boost window is what lets the newest iPhones hit their maximum charge rate before thermal management pulls them back. It is a burst design, not a sustained one: no laptop will see the boost figure for any meaningful length of time, because the request has to be short and the adapter has to be cool. The model detail is on the 40W Dynamic Power Adapter page, and the head-to-head with the older part is 35W vs 40W Dynamic.
The generic version has no such trick. A 40W dual-port charger is a pair of 20W supplies sharing a case, which is genuinely useful — two full-speed phone charges from one wall socket — but it is not a step up in single-device speed over a 20W brick.
What 40W charges
On a single unrestricted port, 40W covers every phone at peak, an iPad Pro at its roughly 30W ceiling, a MacBook Air at normal (not fast) charge speed, and a Steam Deck near its 45W design point. It falls short of a Nintendo Switch dock's 39W only in the sense that the dock wants that power specifically as 15V/2.6A — check for a 15V rail rather than assuming the total covers it. It is well short of any Pro-class laptop, which starts at 67W.
Picks at this wattage
- 40W
Apple 40W Dynamic Power Adapter
Two USB-C ports, 40W rated, with a dynamic boost that targets the fastest supported iPhone charge on a single port.
- Output
- 40W + dynamic boost
- Ports
- 2× USB-C
- Input
- 100–240V
- 40W
40W dual USB-C GaN charger
Class pick for two-phone duty. Compact GaN body, 20W + 20W when both ports are busy; verify whether a single port can take the full 40W.
- Output
- 40W total
- Ports
- 2× USB-C
- Check
- Single-port max
- 2-port
40W-class C+A dual charger
Class pick when a legacy USB-A cable is still in the mix. Same total, with one socket kept on the older port type for accessories.
- Output
- 40W total
- Ports
- 1× C, 1× A
- Note
- A port has no PD
Size up or down from here
Down: 30W single-port is cheaper and gives one device the complete rail set; 35W is Apple's older dual-port part and splits the same way. Up: 45W adds PPS and covers a Galaxy Ultra or a Steam Deck properly, and 65W is where a laptop and a phone can share one brick without either suffering. For the newest iPhones specifically, the device page best charger for the iPhone 17 explains where the dynamic boost is and is not worth paying for.
FAQ
Is the 40W Dynamic Power Adapter worth it over a 35W?
Only if you want the fastest supported charge on a current iPhone. Both are dual USB-C and both split when loaded; the dynamic boost applies to a single port, briefly, on supported devices.
Can a 40W charger charge a MacBook Air?
Yes, at normal charging speed, provided a single port can supply the full 40W. It will not meet Apple's fast-charge specification, which calls for a higher-wattage adapter.
Do both ports on a 40W adapter give 40W?
No. 40W is the total across the adapter. With two devices attached, most units settle near 20W per port, and some cap each port at 20W even when the other is empty.