The black mark is from arcing between the charge port and the connector. If your charge port has debris in it and needs cleaned out the charger connector doesn’t go into the port as it should and arcing can begin. The charge cable should be ok but I’d check for dirt inside the port.
Put the charger into the port, if the plastic part of the charger connector touches the bottom of the phone or very nearly touches then the port is ok.
If there’s a gap of a mm or more then it probably needs cleaned out. I get customers all the time at work with iPhones that need the port cleaned. Common problem with iPhones.