Power is taken from a voltage source, delivered to a load. Power does not go back to the voltage source. IE Current flows from the voltage source to the load, only. IE Current flows from a battery to a motor. The motor can not operate as a generator, and has to coast to a stop.
Power is taken from a voltage source, delivered to a load, or vice versa.
IE Current flows in both directions. IE Current flows from or to a battery when connected to a DC motor that runs in only one direction. The motor can operate as a motor or generator, but the motor shaft turns in one direction. The motor can be stopped abruptly, but not reversed. Power is taken from a voltage source, delivered to a load, or vice versa, AND the voltage to the load can be reversed.