Root cause:
The spark is called as Arcing. When the plug is connected to the outlet, it might spark because the contact area is not enough and the electrical current comes.
So, you might observe tiny damaged traces on the plug. It is normal.
If the sparks are more serious or the outlet is discolored and deformed, please stop to use it and change the outlet or extension cord to ensure safety.
It may be caused by the outlet is rusty or deformed, or affected by moisture, oxidation, stuff, dust...etc.
Solution: Please use a high-quality outlet or extension cord. If the outlet or extension cord has been used for a long time, we recommend you should change it.
Before connecting the AC adapter, please check any foreign material at the plug-in or outlet.