Turntable Power Source Benefits

Many of the table designs today have the motor separated from the platter and run the platter via a belt or string. I see some people are going to DC to power these motors and the Teres site claims them to be a real benefit. Walker makes a regulated power supply that others have said are helpful.

How are they helpful? I can understand how a steady power supply source can provide a more stable way to deliver constant and unvarying platter speed. But how can they improve the sound other than that if the motor is already separate from the platter? If you have the TT plugged into a separate outlet, how can any power-induced problems get into the sound chain? Do motor cycles jump from the motor to the cartridge?

Help!