How do you use a capacitor as a power saver?

You cannot use a capacitor as a 'power saver' or, more accurately, 'energy saver'! A capacitor may improve the power-factor of a load, and this may reduce the value of its load current, but this does not reduce the energy consumed by the load. For a residence, a so-called 'power save' capacitor is nothing more than a rip-off.