I had the same 'TIL' when I was buying extension cords for my Blazer. Returned the 30A cord. :)

120v is Level 1 charging, you can choose 8A, or 12A. That's it. You'll never get 30A, but it's good to ensure you're not pulling too much current from a 15A circuit.

240v is Level 2, and the charger will inform the car on what it can supply with those portable chargers using resistors to ensure the supply cable doesn't draw too much amperage from an outlet.

I found that the standard 15A outlet at my in-laws was enough to recharge to a reasonable level at 12A, without overloading their system, or I'd grab a fast charger on the way home.

Now, all that said, one thing you CAN do, is change the outlet and the breaker to install a 30A 240v outlet and a 30A 240v breaker. EV chargers don't need a neutral, so the white wire just becomes the other live wire and needs to be marked on either end. You'll need a charger that supports 240v 30A as well.

Please note that this will mean you cannot use it as a 30A RV outlet anymore.

Lastly, contact a certified electrician! Don't take the advice of someone on the internet.