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5W vs 20W: the one upgrade that is actually 3×.
Most charger comparisons argue over minutes. This one doesn't. The old 5V/1A cube delivers 5 watts; a 20W USB-C adapter delivers four times that on paper and roughly triples real-world iPhone charging speed to 50%.
Spec sheet, side by side
| 5W (legacy cube) | 20W USB-C | |
|---|---|---|
| Output profile | 5V/1A only | 5V/3A and 9V/2.22A |
| Protocol | None — dumb USB-A supply | USB-C Power Delivery |
| Port | 1× USB-A | 1× USB-C |
| Size class | Small cube, non-folding on most | Same footprint or smaller in GaN |
| iPhone 0–50% | Roughly 1.5–2 hours | About 30 minutes |
| Best-suited devices | Watch pucks, older earbud cases, e-readers | Every iPhone since the 8, AirPods, Watch, Kindle, small Android |
The gap is protocol, not just amperage. A 5W supply can only offer 5 volts; an iPhone's fast-charge path needs the 9V rail, which requires Power Delivery over USB-C. That is why a 5W charger cannot be coaxed into fast charging with a better cable — there is no rail to negotiate. See USB-C Power Delivery explained for how the handshake works.
Where each one still wins
5W wins for trickle jobs. An Apple Watch magnetic puck draws about 5W, and older AirPods cases cap out near 5W too. Plugging those into a 5W brick costs you nothing, so if you already own cubes, keep them on the nightstand for accessories.
20W wins everywhere a phone is involved. An iPhone peaks around 20–27W in the first 20 minutes of a charge; on 5W it never gets near that window and spends the whole session at trickle rate. The same is true of a Kindle, a Switch in handheld standby, and any Android phone from the last five years. Detail per device: what 5W actually charges and what 20W charges.
Verdict: 20W, and there is no real exception
Buy the 20W. Judged on delivered watts for the reader's device it is a 4× spec improvement and roughly a 3× real improvement on an iPhone; judged on protocol it is the difference between having Power Delivery and not having it; judged on cost per watt it is far cheaper per watt than a 5W cube ever was. The only reason to keep a 5W unit in service is as a spare for a Watch puck or an older earbud case, and even then it is a convenience, not a choice. If you're buying today, the more interesting question is one class up — see 20W vs 30W, and 18W vs 20W if you already own an 18W brick.
- 20W
Apple 20W USB-C Power Adapter
The reference 20W. Fast-charges any iPhone from the 8 onward and every AirPods case.
- Output
- 20W USB-C PD
- Rails
- 5V/3A, 9V/2.22A
- Ports
- 1× USB-C
- Value
Amazon Basics 20W USB-C
The budget-bracket certified 20W. Same rails, same iPhone speed, no brand premium.
- Output
- 20W USB-C PD
- Ports
- 1× USB-C
- Certified
- UL listed
- 30W
Anker Nano 30W
The compromise pick: barely larger than a 20W, 50% more headroom, folding plug.
- Output
- 30W USB-C PD
- Ports
- 1× USB-C
- Tech
- GaN
Accessory-only chargers are covered on the AirPods charger page; the full head-to-head index is at charger comparisons.
FAQ
Will a 20W charger damage a device that shipped with a 5W cube?
No. A device that only knows how to draw 5W will draw 5W from a 20W adapter — the adapter offers rails and the device picks one. Nothing is pushed.
Does the cable matter when moving from 5W to 20W?
Yes, in one way: you need a USB-C to Lightning or USB-C to USB-C cable. A USB-A to Lightning cable plugged into a USB-A charger cannot carry the 9V fast-charge rail regardless of the adapter.
How much faster is 20W on an iPhone in practice?
About 50% charge in 30 minutes versus roughly 1.5 to 2 hours on a 5W cube. The advantage shrinks after 80%, where every iPhone deliberately slows to protect the battery.