With the MagSafe Charger, Apple has taken a similar strategy as Xiaomi with its first 5G phones, where the Xiaomi 30W Qi Wireless Charging Stand provides fast wireless charging only with the Mi 9 Pro 5G. The MagSafe Charger is providing only faster charging with iPhone 12 models and older phones like the iPhone 11 Pro Max is only getting 3-3.5W of power.
Using the GRL-C2 USB PD Tester and GRL-PSP Power Analyzer software from Granite River Labs, we can see that the MagSafe Charger is consistently pulling about 5W from its USB-C cable, resulting in about 7.9 hours for the iPhone 11 Pro Max battery to charge from 0% to 77% (with the phone's display kept off). Interestingly, at 77% battery, the MagSafe Charger automatically stops charging the iPhone 11 Pro Max.
Unlike the iPhone 12 , the iPhone 11 Pro Max does not have MagSafe magnets to easily align the Qi wireless charging coils so it took some trial and error to find the optimal location to place the MagSafe Charger on the back of the phone.