Apple USB-C power adapter volts, amps
The following is a partial reference of Apple USB-C power adapter compatibility; of voltage, amperage, and wattage ratings, and of specific Apple USB-C devices.
Use the charger that came with your iPhone, iPad, MacBook, HomePod mini, etc., device. Higher-wattage USB-C chargers than that shipped will usually work, if the higher-wattage charger offers the necessary voltage and sufficient amperage. Which is what this tip lists.
Voltage (V) and amperage (A) ratings for common Apple USB-C power adapters:
18W: 5V3A, and 9V2A
20W: 5V3A, and 9V2.22A
29W: 5.2V2.4A, and 14.5V2.0A
30W: 5V3A, 9V3A, 15V2A, and 20V1.5A
Ratings for some Apple USB-C devices:
HomePod mini: 9V2.22A, will tolerate 9V2A
The Apple 29W adapter is problematic for most uses beyond its intended Mac models. 29W is not compatible with HomePod mini, for instance. 30W should work fine.
More Info
Information here will be updated as now chargers and information on existing chargers becomes available. Updates are welcome, as I don’t have a full set of Apple chargers.
Apple USB info: What is USB? - Apple Community
USB-C: https://en.wikipedia.org/wiki/USB-C
USB-A, USB-B: https://en.wikipedia.org/wiki/USB_hardware#Connectors
Connect and use other storage devices with Mac - Apple Support
Use a power adapter with your Mac - Apple Support
About Apple USB power adapters - Apple Support
Additional information: https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery