Demystifying Apple's USB-C charging

Published

Apple sells three different models of USB-C chargers and includes them respectively with their three Macs:

Model  Charger
Macbook  29W through 14.5V at 2A
Macbook Pro 13''  61W through 20.2V at 3A (and fallback 9V at 3A)
Macbook Pro 15'' 87W through 20.2V at 4.3A (and fallback 9V at 3A)

So there are now several USB-PD (Power Delivery) available from Apple, at three different voltages. In nearly all cases the higher wattage should be better but there are interesting differences.

Macbook (2016)

The Macbook supports charging at 20.2V and 14.5V respectively. However, the larger charger doesn't actually help this model, since it draws less power at the higher voltage to equal the ~28W of the stock charger:

Charger Measurement
29W model Macbook charging with 29W charger
61W model Macbook charging with 61W charger

I've also tested a 5V 3A power bank and the Macbook can also charge at that voltage, though only giving it 15W.

Macbook Pro 13'' (2016)

No surprise here that the Macbook Pro charges faster with the charger that was delivered with it but it's important to note that you can charge it with the smaller one just fine and there is a significant difference in size and weight (approx. 120g vs 200g), which makes the 29W model a great alternative for business travel.

However, if the battery isn't fully charged and you are putting the machine under heavy load, it will complain constantly that there isn't enough to charge the laptop (charging mode can toggle on and off).

Charger Measurement
29W model Macbook Pro charging with 29W charger
61W model Macbook Pro charging with 61W charger

iPad Pro 12.9'' (2015)

The iPad Pro is an interesting outlier since not only does it support the 5.2V profile but also the 9V and 14.5V profile but it cannot do the 20.2V.

This means that the iPad can actually be charged faster with the smaller charger:

Charger Measurement
29W model iPad Pro charging with 29W charger
61W model iPad Pro charging with 61W charger

Summary

I did not have a 87W charger at hand to play around with and presumably it could still charge at least the Macbook Pro faster but I don't think the additional cost will actually have much of an impact.

My takeaway from the comparison is that the cross-device compatibility is great and I'll likely only travel with the 29W model and use the 61W when stationary for the Macbook Pro.