Definitely better to charge an EV with clean energy. But it's probably better to charge an EV with dirty electricity than it is to keep using a combustion vehicle.
IIRC a gas vehicle is something like 20% thermally efficient, whereas a coal/oil power plant can be up to 60%. So even if my EV is charging off oil or coal, I'm getting 3x the energy per unit of emissions compared to a gas vehicle (though who knows how that translates to miles of range).