I am not judging your repair skills.
I am just posting a warning since others might not test their power supply and check the mobo capacitors before they force start the supply bridging the "/power on" pin to GND. (On the supply connector)
You say you checked the ESR of the capacitors on the mobo. Is that something you can do leaving them in the circuit?
If so, what ESR meter are you using?
If you have multiple capacitors on the same supply rail, how would the meter be able to test one specific?
Question is, if you have to remove them, isn't it better to replace them right away, knowing that they have a bad reputation?
Usually, decoupling capacitors are connected to large copper areas (the inner power and GND planes of a multilayer pcb.)
Due to that, they don't desolder very easy (Unless you have something to preheat the pcb). As they aren't that expensive, it seems to make sense to take no risk and install new better quality ones right away.
In a perfect world, powering the system using the 2 jumper pin's on the mobo that normally connect to the power switch should work just as well. It's just not always obvious figuring out which pins to use.