Dominikat,
The power regeneration circuit combined with the storage capacity for the electricity the power regen circuit saves, means it is able to draw from another power source, which boosts the overall power the machine has to draw from. So it's not just the engines that provide all of the power. Counterswinging, lowering the boom, etc, are all used to generate electric power from the momentum and such. That electricity is then stored in a series of devices like capacitors to be reused when needed.