NEMA 5-15P to 14-50R for EV Charging, Maximum operationg power of 20 Amp, 125-Volt, 2,500-Watts.EV Charging requires high current for an extended time, it is a continuous load and it must be limited to 80% breaker capacity. Please follow the 80% rules, if your circuit breaker is 20 Amp, please limit the amperage manually to 16 Amp.
If you want to use your Tesla UMC charger with 14-50 adapter plug into 5-15 household regular 15A 120V outlet.
This adapter cord can help you to do it.