Ground Fault Circuit Interrupter (GFCI)

GFCI receptacles or breakers are often found on garage and outdoor receptacles and sometimes on 240V circuits like NEMA 6-20. They trip if they detect very small currents leaking from the hot wire(s) to ground, aiming to protect humans from shocks in fault situations.

It turns out that most EVSEs actually leak a tiny bit of current to ground when they first start charging as a test to make sure the ground pin is actually connected to a useful ground. The EVSE test leaks a small enough or quick enough current such that it won't trip a properly functioning GFCI. But older and weaker GFCIs have been known to trip right at the start of charging and weak GFCIs can also trip during charging as well.

If this happens to you, replace the GFCI receptacle or breaker, and your charging problems should go away.

Note that 120V household GFCI receptacles come in two sizes: 15A or 20A. If you have a 20A breaker protecting your receptacle, then buy the 20A version. It'll be more robust and allow you to charge even faster if you have the appropriate mobile EVSE.