Nothing to do with PSU it self nothing to do with how much current system draws. You can produce flame with AA battery as well.

Looks like just faulty soldering or faulty connectors. Loss of proper connection causes open circuit > resistance closing to infinity thus current without other path will try to flow trough and heat up at point where resistance is high causing connections to catch fire. Might as well be just your own fault if you did not connect wires properly but I would go with cheap connectors used that doesn't fit together too well.