Switch power between two appliances or power strips?
A 3-way switch, A duplex socket, a length of cord with plug and a nice box will do it.

Attach the live from the cord to the common on the 3-way and attach the 2 traveler connections to the live side of the socket and break of that tab. 

Pigtail earth to everything that needs an earth. And make sure there is adequate strain relief where the cord exits the box.

That way if the switch is on one position only 1 side of the duplex gets power, if the switch is in the other position the other side gets power.