They are not the same concept. Rack and pinion is a specific mechanical structure responsible for converting the rotation of the steering wheel into the steering of the wheels; while power steering is an auxiliary system designed to reduce the amount of effort required by the driver during steering.

For light vehicles and small cars, rack and pinion steering systems usually provide sufficient handling performance and driving comfort. For heavy vehicles or large SUVs, power steering systems are particularly important. The weight and size of heavy vehicles make steering operations more difficult.