I was disappointed to find out that Anker power strips can be mounted vertically, but only with the cord at the top. This seems counterintuitive, but that’s also true for every other strip I could find (other than the ones that mount horizontally).
All these strips have a hole large enough for a screw head, and a narrower slot to slide the head in. Why not have slots on both sides, like this: =o=. I found one model that has two slots at 90 degrees, for vertical and horizontal mounting, but none that allows vertical mounting with the cord at the bottom.