PC begins operation immediately upon switching on power.
PC begins operation immediately upon switching on power.
I like to make measurements when possible, and then procede from there. You would need a DVM, but if you're not familiar with it's use, then probably you can't do this. One would measure the voltages at the power supply connector on the motherboard - with and also without a load. Sometimes it's just better to take it to a shop where they have tools and parts to troubleshoot and repair - even though one would like to be able to solve a problem on their own. The correct operation of everything depends on the supplied power, so it's good to be able to confirm that the power supplied is correct with and without a load.
If there might be a power problem, it doesn't seem important right now. If both PSUs work properly, the problem stays. Both are solid products. It's unclear if extra power checks help here.
It seems you're likely right. If the crimp connector on one of the connectors fails, it might point to an issue with something outside those components. We'd then focus on voltage levels and their locations, considering voltage ratings and usage points. My approach is usually to trace problems down to individual parts, though this isn't always the case for everyone.