How Your Mac Picks a Charging Profile: Watts First, Then Volts
A USB-C charger offers a menu of voltage and current options. Across every charger we've measured, a MacBook took the most watts, and broke ties with the higher voltage. An airport seat charger proved the order.
When you plug a USB-C charger into a Mac, the charger sends a menu of profiles, such as 5 V at 3 A or 20 V at 1.5 A. The Mac requests one. USB Connection Information shows that whole menu and marks the one the Mac chose.
After measuring dozens of chargers, the pattern is clear: the Mac takes the most watts first, and the highest voltage second.
Ties go to the higher voltage
Many chargers offer the same wattage on more than one rail. In every case we’ve measured, the Mac took the higher voltage:
| Charger | Same watts offered at | Mac picked |
|---|---|---|
| Anker 33W | 33 W at 15 V and 20 V | 20 V |
| Apple 30W | 30 W at 15 V and 20 V | 20 V |
| Anker Nano 30W | 30 W at 15 V and 20 V | 20 V |
| UGREEN 30W | 30 W at 12 V, 15 V and 20 V | 20 V |
| Monoprice 30W car charger | 27 W at 9 V and 12 V | 12 V |
| Target dealworthy 20W | 20 W at 9 V and 12 V | 12 V |
| Golf ball 20W | 20 W at 9 V and 12 V | 12 V |
| AUKEY 20W | 20 W at 9 V and 12 V | 12 V |
That fits the physics. For the same power, a higher voltage needs less current, and less current means less power lost as heat in the cable and connectors.
But watts come first
Those results can’t tell you which rule comes first, because on every one of those chargers the highest voltage also had the most watts, or tied for it.
A USB-C port on a Zoeftig airport seat broke the pattern:
| Profile | Rail |
|---|---|
| 15 W | 5 V up to 3 A |
| 20 W | 9 V up to 2.22 A |
| 25.5 W | 15 V up to 1.7 A (chosen) |
| 24 W | 20 V up to 1.2 A |
Its 20 V rung offered 24 W. Its 15 V rung offered 25.5 W. The Mac stepped down to 15 V for the extra 1.5 W. So the order is watts first, then volts. The video at the top shows it happening.
What else it ignores
- PPS and AVS ranges. Plenty of chargers we’ve tested offer a PPS range, and some list AVS. The Mac chose a fixed rail every time.
- Anything above its own limit. A MacBook Air M5 accepts up to 72 W. A charger can offer more, but the Mac only takes what it can use.
- Anything the cable can’t carry. Without a 5A e-marked cable, a charger limits its offer to 3 A, so a 65 W rung becomes 60 W before the Mac ever chooses. See the Anker Nano Charger Neo .
Apple doesn’t publish its selection rule. These are observations from one MacBook Air M5 across every charger on this site, and they’ve been consistent so far. If you see your Mac pick differently, USB Connection Information will show you the menu and the choice.