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.