Well, knowing the name of the motherboard would be useful.
Could try an update on the BIOS, but don't think that would be required.... And anyway, why did you go into the BIOS and find this in the first place?
What were you doing to make you notice this? Or more specifically, what did you notice that made you check the BIOS settings?
Yes, +16 volts on a 12 volt rail... I'm surprised its still alive... Although it sounds like someone is trying to overclock.
How did you set it to default? Turn all values to default? If so, you may need to take the motherboard battery out (CMOS) battery and wait some time, put it back in and boot it up again. That should reset all BIOS values back to normal.
Speedfan or other monitoring programs are useful in Windows. Linux, they should have their own terminal applications to do the same thing.