Wattage · The first PD step
18W adapters: 9V at 2 amps, the step 20W replaced.
18W was the number on the first generation of small USB-C PD bricks and on every Quick Charge 3.0 adapter. It is two watts and one rail away from today's 20W standard — which matters far less than the spec sheet suggests.
Three rails behind one number
A typical 18W USB-C PD adapter advertises three fixed profiles, and the device picks whichever suits its charge IC:
| Rail | Power | Who requests it |
|---|---|---|
| 5V / 3A | 15W | Accessories, low-battery trickle, anything without PD |
| 9V / 2A | 18W | Phones — the headline rail on almost every device |
| 12V / 1.5A | 18W | Older Quick Charge 3.0 hardware, some dashcams and hubs |
Apple's A1720 18W USB-C adapter shipped in the iPhone 11 Pro and 2018 iPad Pro boxes; Qualcomm's Quick Charge 3.0 headline figure is the same 18W, which is why the two eras collided at this wattage. The difference is protocol, not power — see Quick Charge explained and USB-C PD explained.
Devices where 18W is still exactly the spec
Meta Quest 3 ships with an 18W adapter and charges at that rate — buying more watts changes nothing on the headset. Pixel 3 and 4-era phones negotiate 18W USB-PD as their maximum. Most Quick Charge 3.0 Android phones from 2017–2020 peak here too, as do a large share of portable power banks, whose input boards are 18W-limited. For those, 18W is not a compromise; it is the ceiling.
18W vs 20W, honestly
A 20W adapter adds one thing: a 9V/2.22A rail instead of 9V/2A. That is 11% more current on the same voltage. On an iPhone the practical gap is a minute or two to the 50% mark, because the phone's own thermal and state-of-charge curve dominates long before the adapter does. The reason to buy 20W today is availability and price, not speed — the full breakdown is on 18W vs 20W.
Picks at this wattage
- 18W
18W-class USB-C PD wall charger
Class pick for Quest 3, older Pixels and power-bank input. One USB-C port with 5V/9V/12V fixed rails and a folding or fixed plug.
- Output
- 18W PD
- Port
- 1× USB-C
- Rails
- 5V/9V/12V
- QC 3.0
18W Quick Charge 3.0 USB-A charger
Class pick for QC 3.0 Android hardware that predates USB-C PD. Same 18W, entirely different negotiation.
- Output
- 18W QC 3.0
- Port
- 1× USB-A
- Protocol
- Quick Charge 3.0
- 2-port
18–20W dual A+C travel charger
Class pick when one wall socket has to feed a phone and an accessory. Confirm the total rating: many split to roughly 12W + 5W when both ports are loaded.
- Output
- 18W class total
- Ports
- 1× A, 1× C
- Check
- Shared total
Size up, or stay here
Stay at 18W if your device's own maximum is 18W — extra watts are wasted on a Quest 3 or a Pixel 4. Size up to 20W for any current iPhone, 25W to reach Samsung's Super Fast Charging threshold, or 30W if a tablet or a MacBook Air is anywhere in the picture. Step down to 12W only for USB-A accessories. Apple's own version of this brick is documented on the 18W USB-C adapter page.
FAQ
Is 18W fast charging?
Yes, by the original definition — it uses a 9V rail rather than 5V, which is what triggers fast charging on phones of that generation. It is simply one step below today's 20W to 30W norm.
Will an 18W charger work with an iPhone 17?
It will fast-charge it, just not at full speed. Current iPhones peak in the low-to-mid 20W range, so an 18W adapter runs them at roughly three-quarters of their maximum rate.
Can I use an 18W USB-A Quick Charge brick on a USB-C phone?
It will charge at 5V through an A-to-C cable, but it will not fast-charge. Quick Charge over USB-A and USB-C PD are different negotiations, and modern phones only implement PD.