I'll try and make this simple. The bottom line is that a car can't handle SAE DC fast charging unless it was designed to do so.
Why?
The prior SAE standard was about "level 1" and "level 2" charging which is all AC, not DC. To use fast DC charging, the car needs:
1) to know what to tell the DC charger to tell it how fast to charge, when to slow down, etc. This is a "control protocol". Without this, the charger will burn out something in the car. Essentially the car and charger need to understand a common language. The language for SAE level 1 and 2 charging is different from the language used to control SAE DC charging. DC charging needs a richer control language so the car can tell the charger what to do and when to keep the charger charging fast but so fast that it burns out the car's battery or charging circuitry.
2) to be able to talk to the charger (electrically) in the first place. The car and charger need the moral equivalent of a phone line so they can talk to each other. I don't know if this is the same or not for SAE AC and DC charging. But it doesn't really matter because of #1 and #3.
3) the proper charging circuitry so the car can safely swallow the power sent by the charger. SAE level 2 charging is electrically different from SAE DC fast charging so the car needs different power paths from the charging port to the battery to handle both.
So if the car isn't designed ahead of time to support SAE level 1 and 2 charging and SAE DC charging, the odds are essentially zero that you can practically and safely retrofit the car to do so. The car manufacturer might be able to develop and produce a retrofit kit but the cost to do so would be high enough that it's simply not worth it. The cost to the consumer for the kit+installation would likely be so high that it wouldn't make financial sense.
About "Supercharging":
Tesla's proprietary fast DC charging (aka Supercharging) is supposedly compatible enough with SAE DC charging that Tesla should be able to provide a reasonably priced adapter. But that's because Tesla knew enough about the SAE standard in advance (and probably influenced it) and designed their charging circuitry and control protocol to be compatible. But Tesla has a nicer plug
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I believe that SAE and Chademo (a competing DC fast charging technology used by the Nissan Leaf) isn't compatible even though both are DC. #3 is probably (close enough to) the same for both. As I understand it, the challenge is #1 and probably #2 -- the control protocols are different enough as is the communication connection that a car can't handle both unless it was explicitly designed to do so. To my knowledge, no car in existence has been.