I'd focus on the floppy drive.
You got smoke, and a power cable lead shows signs of substantial overheating in a short time period. That only happens because a VERY large current waq flowing through the line. Now, that could happen if the supply voltage was 'way too high, but let us remember that the same voltages are supplied from the PSU to several devices. So if the PSU output is at fault, you should have seen a similar problem in other places. On the other hand, excessive current can be pulled because the floppy itself either had a fault or was mounted incorrectly, and there was a near-short circuit. Or maybe this condition could happen if you plugged the connector in wrong at the floppy. But either way, very high current was flowing through some parts in the floppy drive. That means it either had a bad component to start with, or it could have developed a bad flaw as a result of any misconnection of the power leads. Maybe you should not use that floppy drive again.
For the damaged power lead, I agree you should not rely on it. Tie it up, tape it off, or whatever to make it un-useable. Or consider replacing the one piece of wire that is burned so you still have that power connector to use after the repair.