I can confirm this. Our Model 3 doesn't charge as fast using a NEMA 14-50 plug connected via the Tesla-provided mobile charger.
When we moved to a new house, we bought a Tesla wall charger, and it indeed charges at higher amps, but I don't know if the extra speed has necessarily been worth it since we primarily charge the car overnight.
When we moved to a new house, we bought a Tesla wall charger, and it indeed charges at higher amps, but I don't know if the extra speed has necessarily been worth it since we primarily charge the car overnight.