This school laptop charger has some data on the side. Suppose mains input voltage is 230V. It says input current is about 1.5A. That's a power of 345W. It says output voltage is 19.5V at 4.62A. That's a power of 90W. It would give the efficiency as 26%. Wow! There must be something wrong with yesterday's substation numbers because they would give an output current in the tens of thousands of Amps.
