Wow. That's not correct. It's the very fact of what the onboard charger does is why they do use those same units. They convert AC power to DC.They are certainly not made of the same parts, or chargers that are in our cars, If they were we would not need DC fast chargers.
This was talking about the version2 Superchargers, and that is a known and confirmed fact from years ago that inside the Supercharger cabinets really is a stack of the same onboard chargers that are installed in the cars. It just groups them so you can process 120kW instead of just 10kW, for example. Here are some thread posts about it from back in 2014 and 2017.
Whats in those Superchargers
Finally 120KW Supercharging!
I don't think we have much information about what's in the version3 Superchargers, and with them being so much higher power, they may be using a different system for the internals of those.