Monoprice 30W USB-C Car Charger on a MacBook Air: Measured
Monoprice's 30W USB-C car charger measured on a MacBook Air: 24 W delivered. Its highest advertised profile is 27 W, not 30, and it runs the older USB PD 2.0 with no PPS.
Monoprice’s 30W single-port USB-C car charger, tested against a MacBook Air with a low battery, per the methodology. Like every car charger in this series, it was run from a USB-C to 12 V socket adapter.
The numbers
| Rated | 30 W |
| Negotiated | 27 W (12 V up to 2.25 A) |
| Live draw | 24 W (11 V at 2.18 A) |
| Protocol | USB PD 2.0 |
| Identifies as | nothing - shows as “PD Charger” |
Profile menu:
| Profile | Rail |
|---|---|
| 15 W | 5 V up to 3 A |
| 27 W | 9 V up to 3 A |
| 27 W | 12 V up to 2.26 A (active) |
No PPS.
30 W is a ceiling, not a profile
The highest rung this charger advertises is 27 W. There is no 30 W entry anywhere in the menu, so there is no way for any device to negotiate 30 W from it.
That is not a defect, and it is not really a lie either. A charger’s headline rating usually describes what the internal supply can produce, while the profile menu describes what it is willing to offer over USB Power Delivery. Designers leave headroom between the two for heat, efficiency and tolerance. The gap here is three watts.
It is a tidy illustration of why this series reads the menu rather than the label. The box number is a claim about the hardware. The profile list is a contract the charger is prepared to honour.
An older Power Delivery revision
This one negotiates USB PD 2.0 rather than 3.0. That explains the missing PPS range: the adjustable Programmable Power Supply mechanism arrived with PD 3.0, so a PD 2.0 charger has fixed rungs and nothing else by definition.
PD 2.0 is not rare in this series - Apple’s 61W and 87W adapters both negotiate it too. For fixed-voltage charging it works exactly as well; you simply lose the fine-grained voltage tuning that modern phones like.
Where it stops
The ladder ends at 12 V. With no 15 V or 20 V rail there is no laptop-tier rung, so the Mac settles on 12 V and draws 24 W, the voltage sagging to 11 V under load. On a MacBook Air that is a genuine, if unhurried, charge.
Related
- How many watts does your Mac actually need?
- A USB-C to 12V car socket adapter: which chargers work - the adapter powering this test
- Testing methodology · Charger database