These are not DC power supplies, thats whats inside the car, a boost DC power supply converting 240v AC to 400v or 800v DC, thats what regulates current and vol

These are not DC power supplies, thats whats inside the car, a boost DC power supply converting 240v AC to 400v or 800v DC, thats what regulates current and voltage to the batteries. If the AC "charger" attempted to regulate current by varying voltage the actual onboard charger would just attempt to pull more current to make up for the voltage drop and probably trip the whole thing. There would be no point in regulating the AC current, it would make the charger very complicated and expensive replicating much of whats in the DC converter/charger in the car. A full DC charger like at a charging station does do this because it is the actual charger bypassing the cars small internal DC charger with DC leads going directly to battery at full pack voltage.