A 2004 AirPort Express as a MacBook Charger: Measured

The USB-A port on Apple's first-generation AirPort Express, measured on a MacBook Air M5. It advertises a full 7.5 W charging profile and delivers 3.3 W.

The USB-A port on a first-generation AirPort Express (A1084, 2004), tested against a MacBook Air M5 with a low battery, per the methodology. Twenty-two years separate the two devices.

The numbers

Rated8 W advertised (nothing printed on the unit)
Negotiated~8 W (5 V up to 1.5 A)
Live draw3.3 W (4 V at 0.83 A)
ProtocolUSB BC 1.2

Profile menu: one entry - ~8 W (5 V up to 1.5 A). There is nothing to negotiate.

It promises the full amount

This is the surprise. The port does not present itself as a plain data socket — it advertises the full USB Battery Charging 1.2 charging profile, 5 V at up to 1.5 A. That is 7.5 W, the same contract the desk power strip offers, and the same one the Anker PowerDrive 2 Alloy offers.

Those two go on to deliver 7.4 W and 7.1 W. This one delivers 3.3 W — less than half of what it just agreed to.

The rail is what gives out

Look at the volts. USB specifies a downstream port between 4.75 V and 5.25 V. Under load this port sits at 4 V, three-quarters of a volt below the floor.

And look at the current: 0.83 A, barely over half the 1.5 A the contract allows. The Mac is not being throttled by the standard — it is drawing what it can get before the voltage falls away underneath it. A rail that cannot hold 5 V cannot deliver 7.5 W no matter what the negotiation promised.

This is a 2004 router doing a job it was never asked to do. The port existed for AirPort Disk and USB printer sharing — you plugged in a printer so the house could print. A printer idles at almost nothing and draws in short bursts. A MacBook pulls steadily and does not stop, and the twenty-two-year-old supply behind the socket was never specified for it.

Honest versus optimistic

Put it next to the DJI drone remote, the other non-charger port in this series, and the contrast is the useful part:

AdvertisesDelivers
DJI remote500 mA (BC 1.2 data-port tier)exactly 500 mA at 5 V
AirPort Express1.5 A (BC 1.2 charging tier)0.83 A at 4 V

The remote promises very little and keeps its word precisely. The router promises the full charging profile and cannot hold it up. Neither will charge a laptop, but only one of them is telling you the truth about why.

Nothing in USB negotiation verifies a claim. A source states what it can supply and the Mac believes it. Whether the rail actually holds is not part of the conversation — it only shows up in a live reading of the delivered voltage, which is the entire reason to look at volts rather than watts.

What it does to a MacBook

Nothing useful. An M5 Air idling with the display on draws several times 3.3 W, so the battery falls while the cable is plugged in. macOS reports a power source attached, which is the confusing part: something is connected, and the battery drains anyway.

The general rule

A USB-A port on a device that is not a charger will give you somewhere between 2.5 W and 7.5 W, and the advertised figure is the ceiling rather than a promise. Monitors, keyboard hubs, routers, airline seats, hotel nightstands, drone remotes. None of them will charge a laptop, and none of them are broken for failing to.

If a port cannot tell you its wattage, assume 5 W. If it can tell you, check the volts anyway.