My thinking was go to Homedepot/Lowes and buy a thin gauge piece of sheet metal, something like 6-10" x 24", 22-28ga. Bend it along the long edge to form a 3 sided "box" to fit over the connectors, with the solid sides to the left, right, and front of the outlet. It will probably be steel grey so paint it to taste and then figure out a way to attach it under the shelf and over the outlet/plugs.
Another thought occurred to me as well, don't laugh. Go to Walmart/Target/local craft shop and buy a wicker or plastic waste basket, any color, that is at or right below the shelf height. Then either cut out a section of the back, the entire back, or cut it in half vertically so that the it sits right up against the wall under the shelf with the plugs "hidden" in it. I can't tell how high the shelf is so this idea might not be feasible.
If you can't find a waste basket the right height you could buy a 12" diameter sonotube. Cut it to height, cut it in half lengthwise, paint it and use it as a faux column under the shelf to hide the stuff.