The computer runs on how many volts of DC power internally.
Line noise is the small variations in the voltage of the power line.
If the PC is plugged into the circuit alone few problems exist, however, if the circuit is shared with a heavy piece of equipment it could cause major problems. Power surges which are a power spike or over voltage occur when major problems occur in the power grid, power surges may increase to 1000 volts or more. Brownouts are undervoltage and are caused when power drops below normal levels, which is common at heavy load times. Brownouts have the potential to do major damage to your computer.