Thanks for this. I thought I was going crazy because it seemed like the USB ports had varying power. This explains a lot.The USB ports can supply up to around 2.4 amps of power, but they are smart usb ports. If they can't detect what kind of device it is (phone, tablet, usb stick, etc) they supply the default USB 2.0 spec of around 500ma. The Garmin is seeing this as a PC, so it defaults to low power pc connection mode. However, I've had luck powering garmins where the proprietary cable broke, through the usb port. However to do this I had to either use a Garmin micro usb supply from a newer gps, or hunt down a special "charge only" cable that has the data pins shorted. This is how USB devices decide what's hanging off the other end of the cable. USB-C is a totally different animal. I'm not sure if Mazda has these usb ports set up to detect these cable though.
Thanks, I was hoping to avoid using the 12V and having a cable dangling. The USB on the dash should be usable... I know my Garmin can be powered by USB connected to a charger but it was weird that it couldn’t charge from the Mazda USB. I guess I’ll try a data blocked USB next and if that doesn’t work, then the 12V adapter is the last resort.My Garmin has a 12V adapter for using in the car, the USB is only used on a computer for updates.
Get a 12V usb adaptor and use the accessory socket as it take up 10A and 120w.