Alright with my trusty kill-a-watt (yes I know it's not as accurate as USB amp meter), I did some experimentation with my Mini 5. With the stock 12 watt with USB A-Lightning it draws 15 watt max which I assume is due to power loss between 15-12 watt. Using my iPP 12.9 18 watt charger with Apple USB C-Lightning cable draws 20 watts - same as my iPP 12.9. So yes, CONFIRMED the Mini 5 does fast charge at 18 watts (at least faster than 12 watt max with USB A-Lightning can muster). I then tried it with my rMB 29 watt adapter and it's drawing about 23 watts so about 21 watts max. I haven't done time testing to see how much it's shaving off vs the standard adapter.