On Jan 9, 11:48*pm, den wrote:
It looks as if someone plugged it into a different socket, proving
that the low resistance (bad connection) is in the plug. When taking
apart the plug observe the terminal condition. *As mentioned
previously the wire to spade connection was probably compromised. Cut
off at least 4 inches to find bright copper, install a NEW plug maybe
soldering, or crimping on a spade, tighten securely, and plug it into
one of the unburnt sockets. Feel the appliance wire for abnormal
temperature. Observe any and all safety procedures.

I see this all the time at my job / business.

Bad plug melts and burns damaging both receptable and plug, high
resistance heating.

Replace both plug and receptable check for heated wires at receptable
too. cut wire back from plug overheated plug wire will not connect
well and lead to futher overheating. coppewr tends to look dark.