We're in the middle of installing a dozen or so APC cabinets in our server room, a complete replacement of all existing cabinets and racks. APC cabinets (like many others) have what they call "0U" slots on the sides of the rear of the cabinet, for hanging things like vertical power strips, or cable-management trays. There are two on each side, an "inner" and an "outer", with the outer being closest to the rear doors of the cabinet, and the inner being closest to the vertical rails of the cabinet itself.
Our initial design called for the inner slots to be vertical cable-management, and the outer slots to be vertical Power Distribution Units (PDUs). The thinking at the time was that the power cable would come in from the server horizontally, go directly into the vertical cablemanagement, and come out to the outer-mounted PDU where it needed to. It seemed like a great idea on paper.
However, for those of you who some day go to design these things, don't do it. It simply doesn't work (it so doesn't work, that as I type this I have our two student interns correcting every one of our cabinets to fix the problem). The reason it doesn't work is because the prongs from the vertical cable-management (which hold the cables) extend too far horizontally. Initially, we thought the limit of the effect of this was that they sometimes can interfere with the horizontal cable-management rows, but that was something we could work around easily enough. Worse, though, is that we found out this morning that they also interfere with the servers' rails, if those rails extend at all past the rear vertical rail (which often happens).
So, learn from my experience -- PDUs on the inside, cable management on the outside. Your life will be a lot easier, even if does mean that your power cables cross the PDUs to get to the cable-management.
UPDATE: Ignore all this for reasons to be disclosed later.
UPDATE 2: OK, so here's the deal. If we swap those around, then the rail extensions block the power outlets that are in the PDUs. Also, the circuit breakers at the top of the power strip completely block access to the vertical rail mounting squares. That last part is fine if all I ever mount are quick-connect devices, but if I should ever need to put in capture nuts, I'm screwed.
We've contacted the manufacturer of the gear to find out "what is it that other people do, because surely this has come up before?"
I have had this exact same problem previously. I though the verticle cable-management were the best thing ever, until I pratically used them next to a verticle-mount PDU.
My solution was to get TWO verticle PDUs side by side in these APC VX/SX racks and get 1 foot power cables to run directly into the PDUs without any need for power cable management, since there is plenty of outlets available per RMU.
If I had the space and the money I'd replace my VX/SX racks with their wider versions. I believe the 2, 0U slots face the rear providing plenty of room for wiring and those pesky super-long rails.