Anker 25W USB-C on a MacBook Air: Measured
Anker's 25W USB-C charger measured on a MacBook Air M5: 22.6 W delivered from a two-rung ladder that stops at 9 volts, on a rail measuring 8.4 V under load.
Anker’s 25 W USB-C charger (model A2656), tested against a MacBook Air M5 with a low battery, per the methodology .
The numbers
| Rated | 25 W |
| Negotiated | 24.9 W (9 V up to 2.77 A) |
| Live draw | 22.6 W (8.4 V at 2.68 A) |
| Protocol | USB PD 3.0 |
| Identifies as | nothing - shows as “Power Supply” |
| Cable read | none - “No e-marker read” |
Profile menu:
| Profile | Rail |
|---|---|
| 15 W | 5 V up to 3 A |
| 24.9 W | 9 V up to 2.77 A — active |
Two rungs. There is no 12 V, no 15 V, no 20 V, and no PPS.
A 9 volt ceiling
The ladder stops at 9 V, which is the tier phones use. 9 × 2.77 = 24.93, so the current was sized to land on the rating at its top voltage - the same trick Apple’s 20W cube plays with 9 V × 2.22 A.
A Mac will charge from it, because a Mac takes the best rung offered and asks no questions. But 22.6 W into a MacBook Air is trickle territory: enough to gain slowly while the machine is idle or asleep, not enough to keep up with real work.
The rail is out of spec
Look at the volts. The contract is 9 V. The measurement is 8.4 V.
USB PD specifies a fixed supply within ±5%, which puts the allowed window for a 9 V rail at roughly 8.55 V to 9.45 V. At 2.68 A this charger sits below it - not catastrophically, but measurably outside what the profile it just agreed to promises.
That is why it delivers 22.6 W of a 24.9 W contract. The current is nearly all there; the volts are not.
Its 33 W sibling does everything this one doesn’t
Put it beside the Anker 33W 2-Port , measured on the same Mac, in the same session, through the same cable:
| Anker 25W | Anker 33W | |
|---|---|---|
| Rated → delivered | 25 W → 22.6 W (90%) | 33 W → 31.4 W (95%) |
| Top rail | 9 V | 20 V |
| Rail under load | 8.4 V (out of spec) | 19.9 V (in spec) |
| Names itself | no - “Power Supply” | yes - names its PD chipmaker |
| Shows the cable | no | yes - full e-marker specs |
| PPS | none | 3.3-11 V, up to 3 A |
Same brand, bought for similar money, and they behave like products from different companies.
The one that matters: it hides the cable
The last row is the interesting one, and it is not a small thing.
A USB-C cable’s e-marker chip runs off VCONN on the unused CC pin, and only whichever device owns VCONN can interrogate it. While charging, that is the charger - your Mac is just the sink. The Mac can only read the cable after the charger agrees to hand VCONN over, and under USB Power Delivery that handover is optional.
This charger declines. Its 33 W sibling does not.
The proof is a controlled one: the same cable, on the same Mac, on the same port, minutes apart. Through the 33 W it reports fully - passive, 5 A, EPR. Through this 25 W it produces no cable identity at all, and macOS falls back to assuming 3 A.
Nothing about the cable changed. The charger decided.
So when your Mac says “no e-marker read” on a charging cable, that is not a statement about your cable. It is a statement about whether your charger was willing to let you look. Any tool that reports the absence as a fact about the wire is wrong on exactly this case - and here the wire is a 5 A, 240 W-rated cable being reported as an unknown 3 A one.
Worth buying?
As a phone charger, it is fine - 22.6 W, small, and a phone never wanted more than 9 V anyway. As a laptop charger it is not one, and the absence of PPS means it will not fast-charge an Android handset either.
If you are choosing between Anker’s small chargers, the 33 W is the better buy on every measurement taken here.
Related
- Anker 33W 2-Port - the same brand doing it properly
- E-marker chips explained
- Why only Apple chargers show their name on a Mac
- Testing methodology · Charger database