Well I am glad that things have worked out with the powered USB hub.
Hopefully things will continue to run well with the present setup you have now.
As for checking the motherboard for signs of failure, this can be a very complicated procedure as it involves technical knowledge of how electronic circuits work and having the right test equipment on hand.
All the average computer owner can do is inspect the motherboard for obvious signs of failure which is burn marks on circuit boards and leaking or bulging electrolytic capacitors.
The power supply is best serviced with a VOM meter. However, there is only so much you can check for on the external side of the power supply.
Power supplies have dangerous amounts of electricity stored inside, that can cause serious burns or electric shock to the inexperienced repair person who attempts to service such a device.
Readings using a VOM meter are possible on the low current DC voltage wire harnesses that exit the unit.
You need basic wire codes and a description of the plugs pin-outs which are located at the end of those harnesses.
A service manual is required to make an accurate analysis, however I can point you to a web site to which there is a basic wiring diagram for most power supplies.
Here is the link. http://www.playtool.com/pages/psuconnectors/connectors.html
I hope this helps you if you decide to do further diagnosis on either the motherboard or the power supply.
Make sure you heed my warning if you decide an attempt at servicing the internal section of the power supply.