The cause of incompatibility issues with Apple’s USB-C chargers has been identified. The reason why a 29W charger cannot charge a device that consumes only 15W is the dispute between these two devices over voltage and amperage.
Many users may not know which devices Apple’s USB-C chargers cannot charge and which ones. For example; According to a report in 9to5Mac, the 29W charger cannot charge the MagSafe Duo even though it can only draw 15W.
Another example can be seen in the charger that came with the iPhone 11 released last year. Apple’s 18W charger that came with the iPhone 11 failed to charge the HomePod mini at first. The company has addressed this issue with a software update released last week.
The problem with Apple’s chargers
One of the reasons for this problem with Apple’s chargers lies in whether or not it supports the protocol known as USB-C Power Deliverey (USB-C PD). For example, the 29W charger does not support USB-C PD 2.0 or USB-C PD 3.0. In other words, while it could provide the power the device could draw, it couldn’t respond to the MagSafe Duo’s charging request.
The same was true for Apple’s 18W charger. The two devices disagreed on the required voltage and amperage. This issue was resolved with a software update that would cause HomePod to prompt for the correct combination.
John Gruber touched on this charging issue in his post on his blog. Gruber said the iPad Magic Keyboard supports 9Vx3A = 27W input, but Apple’s 29W adapter cannot provide it. The reason the 29W charger did not charge the iPad Magic Keyboard was that it had two configurations: 14.5V x 2A = 29W and 5.2V x 2.4A = 12.48W.
The 30W adapter had four different output options. The output of this 30W adapter, 9Vx3A = 27W, could be charged as it matched the iPad Magic Keyboard input. In addition, this problem with Apple’s USB-C chargers also occurs with third-party devices and ‘power banks’.