Odds are that it was not the supply itself that caused the damage but rather worn out PCIe connectors pins on it and/or the miner. Connector pins are good for surprisingly few connect/disconnect cycles, typically I see ratings as low as 25. After that the plating wears off and spring tension drops leading to poor connections. Once that starts things avalanche to burned plugs rather quickly.
Sometimes. One thing I have noticed is that Bitmain uses cheap plated brass plugs, they do not conduct as well as nickel ones but they cost a few pennies less.
And while loose connectors can be a problem I think the bigger problem is voltage sag: If you check the voltage at the miner pins and it's less than 12v then you have voltage drop between the supply and the miner. Aside from being resistance (warming the wires) it results in the miner pulling more current to maintain output. P=I*E, so as voltage (E) goes down, current goes up which stresses the pins even more.
Thus the connector warms up, resistance goes up, and the connector burns. This happens a *lot* on Neptunes running with 500 watt Corsair supplies. Annoying. Then if you have 3 plugs in parallel, one burns, goes high resistance and the current load is distributed across the other two. With the usual results.
Side question is did the ribbon cable burnt: I can see one of the ribbon cable plugs looks melted, if the grounds opened on the final plug before the hots it's possible for the miner to use the ribbon cable's ground as a return, burning that and possible traces on the board.
