If the PSUs voltage on one of its rails is too high, it would be too high for all of the components attached to that rail. Components draw as much power (amps) as they need, neither the PSU nor the motherboard are able to "push" it.
My suspicion would be the exact opposite. The PSU might be faulty and isn't able to supply enough power to all components under load, which is why the system reboots. Which could be e.g. why components attached to USB start to fail, because they no longer get the 5V they need.
You could download HWMonitor. It can show you the voltages. The typical behavior is for voltage to go down as load goes up.
