Apple's new MagSafe Charger can wirelessly refill your iPhone 12 series device at speeds up to 15W, but if you're opting for the iPhone 12 mini, your max charging speed will be just a bit slower.
An Apple support document has revealed that the MagSafe Charger will top out at 12W of power delivery when used with the iPhone 12 mini rather than the 15W supported on other iPhone 12 models (via MacRumors). To get 12W of charging on the iPhone 12 mini, you'll need to plug the MagSafe Charger into a USB-C wall charger that's at least 9V/2.03A.
Meanwhile, higher wattage wall chargers at 9V/2.56A or above will deliver up to 15W of power to the iPhone 12, iPhone 12 Pro, and iPhone 12 Pro Max.
Getting 12W of wireless charging is still quite a bit faster than the 7.5W that the iPhone used to top out at. And while the iPhone 12 mini may not get the same 15W of wireless power as its bigger iPhone 12 siblings, lots of folks who are buying the iPhone 12 mini likely will be willing to make that tradeoff to get the much smaller device.
Apple's MagSafe Charger support document also notes that if you've got Lightning accessories like headphones plugged into your iPhone 12 device, wireless charging will be limited to 7.5W to comply with regulatory standards. So if you plan on listening to music while your phone is charging, you may want to use wireless headphones or the phone's built-in speakers.
Finally, Apple says that it's important to plug your MagSafe Charger into a wall charger before placing your iPhone on it. This will allow the MagSafe Charger to verify that it's safe to deliver the maximum amount of power. If you put your iPhone on MagSafe first and then plug it in, just remove the iPhone, wait a few seconds, and then put it back on to get max power.