An EVSE internally from the factory (sometimes it is user adjustable, and sometimes, it is adjusted automatically if it 'sees' one of it's special adapter plugs) is set to announce a maximum output in amps to the vehicle. A level 1 EVSE is designed to only work on 120 +/- a certain range of voltage. A level 2 EVSE is designed to work on 240 +/- a certain voltage. Unless modified internally, and most are not user adjustable, they output a specific signal that tells the connected vehicle something like "I have 30A max available". It is the VEHICLE that then decides how much power to try to pull from the EVSE. The EVSE is just a moderately smart on/off switch. The EVSE does NOT adjust itself, except in fairly rare cases.
2011 535i x-drive GT, 2014 i3 BEV