The USB Port on a Desk Power Strip on a MacBook Air: Measured
The USB-A port on a no-name desk power strip, measured on a MacBook Air M5: 7.4 W, no Power Delivery, and a ceiling set by a 2010 charging standard.
The USB-A port built into a generic desk power strip, tested against a MacBook Air M5 with a low battery, per the methodology. No brand, no rating printed anywhere - just a USB port most people never think twice about.
The numbers
| Rated | none printed |
| Negotiated | USB BC 1.2 |
| Live draw | 7.4 W (5.2 V at 1.43 A) |
Profile menu: none. There’s nothing to negotiate.
Why 7.4 W is the ceiling
This port has no USB Power Delivery at all. With nothing to negotiate, the Mac falls back to the oldest standard the two share: USB Battery Charging 1.2 (BC 1.2), whose dedicated-charger mode allows up to 1.5 A at 5 V. 5 V × 1.5 A = 7.5 W, and the measured 7.4 W is that ceiling in practice.
That standard dates back to 2010. Every generic USB port like this one - in a power strip, a hotel nightstand, an airport bench - is almost certainly still running it. They were designed for phones of that era, and they’ve never needed to change.
What it’s good for
A phone, overnight. Genuinely nothing else. A MacBook will charge from it - 7.4 W is enough to hold the battery or gain slowly while the machine sleeps - but it’s the slowest path in this entire series. Plug a laptop into a power strip’s USB port expecting real charging and you’ll be disappointed.
The lesson generalises: a USB port with no wattage printed on it, and no Power Delivery, is a 7.5 W port. Assume that, and you’ll never be surprised.