Not exactly half the speed, but that the vehicle needs to boost the voltage coming from the charger in order to charge the battery. For some cars this is limite

Not exactly half the speed, but that the vehicle needs to boost the voltage coming from the charger in order to charge the battery. For some cars this is limited to around 100kW, way less than charging the battery from a sufficiently high voltage directly. For high end cars like Porsche Taycan you can configure the rated wattage of this DC-DC converter.