US Version: https://www.apple.com/shop/product/mw2n3ll/a/power-adapter-e...
The big recess above the pins is what encases the button of the charger and provides grounding if it includes metal strips. Assuming the charger itself has a metal button.
In the EU a grounded cable has been the default forever (I have a grounded cable from my 2010 MBP which I use as travel cable for my 2021 MBP)
Some heat is normal, but the sparking seems concerning.