Thank you. The charger that came with the bike has instructions whcih say to plug into battery first, THEN to outlet. It never causes a spark.
I have also connected that original charger to the wall outlet first and then to the battery, and that doesn't cause a spark either.
Also the instructions on the AliExpress charger say to plug to the battery first.
I guess that means my original charger is better quality.
For my AliExpress complaint I would have thought that the company would say a spark is normal for their charger if it is normal under their own stated method in the instructions. The pic I showed them was with the power cord to outlet still wrapped up, so their response wasn't in sync with the alternative procedure, of plugging to wall outlet first.
Since you guys report that sparking is not a sign of malfunction in your experience, I guess I will just put the new charger aside for backup in case my old charger fails.
Thanks, guys.
Later... I tried plugging the charger into the outlet first, contrary to instructions. Confirmed, no sparking.
Still, isn't insurance coverage nullified or questionable if you do the opposite to the electronics safety instructions?