You might think that Apple’s 29W power brick would be more than capable of powering both an iPhone 12 and Apple Watch on the MagSafe Duo charger. The combination of devices can, after all, be charged using as little as 15W. But this isn’t the case – you instead need the replacement 30W power brick …
AppleInsider spotted the information in a new support page. This starts out by saying that a power brick of 20W or more is enough.
Use the included USB-C to Lightning cable to plug in your MagSafe Duo Charger to a recommended 20 watt (W) or greater Apple USB-C power adapter* or a compatible third-party USB-C adapter. You can also connect to a USB-C port on a Mac or PC.
But that asterisk leads to a foot-note:
*The Apple 29W USB-C Power Adapter isn’t compatible with the MagSafe Duo Charger.
The reason? MagSafe Duo requires a protocol known as USB Power Delivery 3.0 (often abbreviated to PD 3.0). The 29W charger predates this protocol. It was replaced in 2018 by a 30W version which does support PD 3.0, and is therefore compatible with the new charger.
The MagSafe Duo Charger is designed to negotiate the maximum power up to 9 volt (V) and 3 amp (A) with a USB PD compatible power adapter. MagSafe will dynamically optimize power delivered to the iPhone. The power delivered to the iPhone 12 at any moment will vary depending on various factors including temperature and system activity.
There are, of course, a wide range of third-party products which support PD 3.0.
Apple’s support page also says you need to power the charger before placing your phone onto it.
It is important to plug into a power source before placing your iPhone on the MagSafe Duo Charger. This allows MagSafe to verify it is safe to deliver maximum power. If you happen to place your iPhone on the MagSafe Duo Charger before plugging into a power source, simply remove your iPhone from the MagSafe Duo Charger, wait three seconds, and then put it back on to resume maximum power delivery.
The company additionally warns about possible cosmetic damage to both case and charger.
If you keep your iPhone in a leather case while charging with your MagSafe Duo Charger, the case might show circular imprints from compression of the leather. This is normal, but if you’re concerned about this, we suggest using a non-leather case.
As with most soft materials, the covering of accessories might experience normal wear over time. The hinge area of your MagSafe Duo Charger might wrinkle over time if kept in the folded position. Leaving your MagSafe Duo Charger in a very hot environment (like the inside of a car on a hot day) in the folded position might lead to more visible, deeper wrinkles in that area. This doesn’t affect the functional performance of the accessory.