Apple 20W USB-C Power Adapter on a MacBook Air: Measured

Apple's 20W USB-C adapter - the little white iPhone cube - measured on a MacBook Air M5: 18.4 W delivered from a two-profile menu that tops out at 9 volts.

The Apple 20W USB-C power adapter - the small white cube sold for iPhones - tested against a MacBook Air M5 with a low battery, per the methodology.

The numbers

Rated20 W
Negotiated20 W (9 V up to 2.22 A)
Live draw18.4 W (8.6 V at 2.15 A)
ProtocolUSB PD 3.0

Profile menu: 15 W (5 V/3 A), 20 W (9 V/2.22 A - active). Two entries, nothing else.

A phone charger running a laptop

There’s no 15 V rail and no 20 V rail here - the rungs a laptop would normally reach for. This adapter’s ceiling is 9 volts, and the Mac charges from it without complaint: it reads the menu, takes the best rung available, and draws power from a rail designed for a phone.

The 2.22 A isn’t arbitrary either. 20 ÷ 9 = 2.22, so Apple sized the current to land exactly on 20 W at its top voltage.

That same figure - 9 V, 2.22 A - is precisely what the HomePod mini demanded at launch, which is why the 18W adapter famously couldn’t run one.

Worth knowing

The Anker 20W Nano Pro returns an identical readout on this same Mac: same two profiles, same 9 V / 2.22 A active rung, same 18.4 W live draw. From the operating system’s point of view the two chargers are indistinguishable.

Buying one

The Apple 20W USB-C Power Adapter is a perfectly good phone charger and an adequate trickle charger for a MacBook Air. For real laptop charging speed you want something offering a 20 V rail.

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