This is one of the more ridiculous ideas in audio, but, to help our nation's economy, I won't discourage people from buying $2,000 magic wires.
However, the suggestion that the power line frequency changes from 60 Hz is completely wrong, and if it were it would have no effect on the DC voltage generated from it. The power transformer might get warmer. No power cord could have any effect on frequency. Power companies maintain tight tolerances not only on on frequency, but also phase, even when the voltage sags due to problems. This is necessary so that different generating facilities can be tied together in a grid, and because many kinds of electrical equipment (eg: clocks) rely on the frequency for a time reference. Actually, once a day, usually around midnight, the power companies go through a brief procedure where the frequency is very slightly modified for a short time as necessary to have the exact number of cycles in one day (5,184,000). If they didn't do this electric clocks would gradually loose or gain time.
However, the suggestion that the power line frequency changes from 60 Hz is completely wrong, and if it were it would have no effect on the DC voltage generated from it. The power transformer might get warmer. No power cord could have any effect on frequency. Power companies maintain tight tolerances not only on on frequency, but also phase, even when the voltage sags due to problems. This is necessary so that different generating facilities can be tied together in a grid, and because many kinds of electrical equipment (eg: clocks) rely on the frequency for a time reference. Actually, once a day, usually around midnight, the power companies go through a brief procedure where the frequency is very slightly modified for a short time as necessary to have the exact number of cycles in one day (5,184,000). If they didn't do this electric clocks would gradually loose or gain time.