I don't have the answer, but I here is my reasoning:
- Cables on the AC side most of the time include earth; so you have 3 wire
- Cable on the AC side are generally standard cable so the are rated for higher power than what the device really need
- The cable on the AC side need to be safe, as even if the power consumed is near the same (in fact it's not true, as the power adapter have a certain efficiency, so the power on the intput side is slightly higher than the output side) if it break you will touch the main, and there will be no limitation.
But on the output side, as the voltage (and current) are regulated and protected, even if you touche the inner wire there is no health risk