A friend of mine saw the following setup/demonstration and he was pretty convinced that can not be right. However, he could not figure out how.
If you know how this is done, he would be happy.
Power(AC) is connect via an energy meter(W), one with a rotating disc visible, to two power sockets(S1 & S2) in the following fashion.
AC-->W-->S1-->S2
When an appliance is plugged into the first socket(S1), the energy meter disc starts rotating quickly.
Now the "energy saving" device is plugged into the socket S2, the rotating speed of the disc is visually observed to be slowed down. If the device is removed, the disc speeds up.
As the energy meter measure power, the device thus was shown to save power via the demonstration.