Some houses have lower voltage than others.  If the connections to
the mains, and the screw-down connectors in the breaker box, are loose or
corroded, the voltage in the house can be low when lots of things are running.
In that case the power will also tend to be noisy, with lots of 'static' imposed
on the pure sine wave.    I'd think the laptop's power supply would run
warmer when the mains voltage is higher, but that probably depends on
the exact circuitry.  (There would be a resistor between the charger and
the battery, and this resistor would be dropping slightly more voltage
when the input is higher.  That's speculation!)

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