Doesn't matter if it is mechanical or electric, both still draw the same amount of power away from the engine. It takes the same amount of energy to move mass either way. To use a electric power steering you would have to install a high amp alternator which will draw more hp from the engine. Basically you just exchange ps pump parasitic loss for greater alternator parasitic loss to power the e assist, same for a electric water pump. Electric fans are only more efficient because there is no parasitic loss when they are off but have just as much loss as mechanical fans when engaged.