Onboard charger
The AC-to-DC converter built into the car that limits Level 1 and Level 2 speed.
Every EV has an onboard charger that converts AC from the grid into DC the battery can accept. Its maximum rating caps how fast you can charge on Level 1 or Level 2, no matter how powerful the wall unit is.
A 7.4 kW onboard charger cannot pull more than 7.4 kW from an 11 kW Level 2 station. DC fast charging bypasses the onboard charger and feeds the battery directly, which is why Level 3 speeds are much higher.