Part of my business is doing electrical repairs for property management firms. Often, between tenants, minor repairs are necessary.
Several years ago, I found that someone had added a light to a small closet under the stairs:
As you can see, a cord was run from a receptacle, through a hole in the stair riser:
On a recent return, I found that the light I had removed had been replaced:
Rather than a light, they mounted a receptacle. The black wire you see is stereo wire; the lighter wire is the 6' pigtail feeding the receptacle:
(Sorry for the poor resolution) Also, please note that the pigtail plugs into a power strip mounted on the stairs: