It's impossible to prove a negative, but I think that's false. The highest I've ever seen is 15A, and that's rare. It was also backed up by scary-small wires. What car have you seen with a 20A outlet? Or are you talking about an aftermarket add-on, in which case you have to go to the battery anyway? I was shocked to see that my Tesla is just over 15 which is high, Jeep 10, Smart car 8.
First blurb from Google...
10-amp
Most cigarette lighters run on a 10-amp fuse that allows for 12 volts or 120 watts of power output at maximum. There may be some variance on this depending on your vehicle. Check your owner's manual or the cover of your cigarette lighter socket to find the specific output for your vehicle.