Causes of elevated voltage level on home power line?

I would be checking out the neutrals on your system. The neutral bar actually balances the loads. Somewhere this socket is running in series with another 120 circuit. The circuit is going through some other fixtures and the neutral is weak somewhere. If you disconnect the neutrals all you would have is 240 volts. This is what is happening. Check your neutrals in the breaker panel first and make sure they are all tight. Then check the other wiring. Regards, Dale