The spark appears at the contact point of E-Scooters when plugging the adaptor in is quite normal with the 42V chargers for high efficiency 36V batteries.
This is caused by residual energy from the capacitor inside the charger which reduces the output ripple of the charger to protect the battery.
When the charger is disconnected from the AC power source, the energy (voltage) stored inside the capacitor will remain for 10-15 seconds and get released to 0V. When it connects back to the charging port on the scooter without plugged into the AC power source, the battery inside the scooter outputs the voltage to charge the capacitor inside the charger and that creates a spark at the contact point for a split second. Once the capacitor has the energy (voltage) stored in it, spark won’t appear until the energy is completely released from it.