12w and 5w are interchangeable see link and scroll down to compatibility. Basically 12w can support EVERYTHING on Apple line iPhone and iPad. 5w can support all iPhones and only the 1st gen iPad mini.
rMini uses 10w.
12w= http://store.apple.com/us/product/MD836LL/A/apple-12w-usb-power-adapter?fnode=3c
5w= http://store.apple.com/us/product/MD810LL/A/apple-5w-usb-power-adapter?fnode=3c
rMini uses 10w.
12w= http://store.apple.com/us/product/MD836LL/A/apple-12w-usb-power-adapter?fnode=3c
5w= http://store.apple.com/us/product/MD810LL/A/apple-5w-usb-power-adapter?fnode=3c