I once did a job for someone who had got confused when wiring up an extension lead - he had got sockets on both ends.
Unfortunately, it was also still not long enough.
So he made another lead to extend it.
This lead had a plug on each end, so you plugged it in to the extension, then plugged the other end into the supply.
All very well if you did/undid it in the right order.
I swapped a plug from one lead with a socket from the other, which he thought was a really clever move...