Apple has now confirmed that its discontinued 29W USB-C power adapter is not compatible with the new MagSafe Duo charger.
Notably, the support document confirms that Apple’s older 29W USB-C power adapter is not compatible with the MagSafe Duo, presumably because that adapter does not support the necessary 5V/3A or 9V/1.67A power ratings. As a result, when the MagSafe Duo is connected to the 29W adapter, it can only charge either an iPhone or Apple Watch rather than both devices simultaneously.
Another reason is that the MagSafe Duo is based on the latest USB Power Delivery 3.0 (PD) protocol which wasn’t supported by the discontinued 29W charger. Apple’s 30W charger does support Power Delivery 3.0.
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.
The company notes that the MagSafe Duo charger must be plugged into a power source before an iPhone is placed on it, which lets the charger verify that it’s 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,” Apple writes.
For those wondering, the company’s 30W adapter that has replaced the discontinued 29W power adapter is fully compatible with the MagSafe Duo charger. The old 29W power adapter was discontinued back in 2018. Apple has recently also discontinued the 18W USB-C charger which used to ship in the iPhone 11 and iPad Pro boxes, replacing it with a new 20W charger. That charger is bundled in the iPad Air 4 box and is required to fast-charge your iPhone 12.
The support document also clarifies that both MagSafe and MagSafe Duo chargers limit power delivery to 12W when used with the iPhone 12 mini.