First, this is not RX8, but you all are so knowledgeable and it's baffling me. My wife's 2015 Mazda 6 has 2 12v ports. Neither one works with a USB adapter UNLESS it's under 1 amp. In other words, I can use crappy chargers that don't keep up, but whenever I plug in a quick charge or anything with decent charging power, it acts like nothing works.

Any idea what the probablem might be?

 

Check the interior fuse box to make sure that all the fuses are intact/not-blown and are the correct amperage fuses. Having a fuse that is too oversized can be worse than one too small as you risk serious damage to the wiring that could eventually develop into becoming a fire hazard. Additionally, try a different quick charge unit. Are you testing this with the car on or off? I've heard of some 12vDC adapters for cars shutting themselves off if voltage gets too low in order to not drain the battery of whatever they are plugged into. Also, there are plenty of people on the Mazda 6 forum who know the platform and have factory manuals available, probably a good idea to ask over there. Goodluck