I'm pretty sure "type C" is just the plug. And the USB "format" used for our Lumia 950/XLs etc. are 3.1 (as in USB 3.1)
This a type A plug:
This is a Type B:
And this is a type A > type B:
Type A > type C
The type is the plug, nothing else. There are chargers with a type C outlet (female), and it is those chargers which will say "type C". It's the plug.
Now, whether or not a (standard) type A plug can deliver the amperage is somewhat of an open question. The Type A plug was originally made to carry a maximum of 1A (if I recall correctly) at 5V.
Anyway, if the (single plug) car charger can put out 3A, it doesn't matter if it has a type A (female) plug or a type C (female) plug. That is not important. Of course it matters whether or not the circuitry in it can deliver it to your phone, but "Type C" is not actually a method of charging. It is the plug. And that plug was designed to carry at least 3 amps, but perhaps even more. But you could make a charger with a type A plug that could carry 3A too. In fact, I have one (Anker, I think?).