Speaking in generalities, cable steering has one fairly thick cable that goes directly through the motor's tilt tube and comes out the other side, with a drag link connecting the end of the cable back to the motor's steering arm. Hydraulic steering has two hoses connected to a hydraulic cylinder, which connects to the steering arm. There are several variations of the system. But they all work by pumping oil into one or the other end of the hydraulic cylinder.
Neither of the systems are "Power Steering". You still provide the power via your muscles to steer the motor against the torque. But hydraulic steering and No-Feedback cable steering lock at whatever position it was at when you stopped turning the steering wheel, so you don't have to constantly hold it against the torque. Yes, they automatically unlock immediately when you again turn the wheel.