My 2012 Equinox has 3 Accessory Power Outlets. The one under the CD player does not work. Could it be the fuse?

Without an expensive test kit there is no way to properly test a relay. The best way would be to swap out a known working relay.
Now to address your issue, the 12v accessory outlets are not driven by a relay. They are connected via your ignition (similar to the radio or glove box light). Since they are all not working I would say that they possibly share a common ground point and that has been disconnected, or that they share multiple fuses. There could be a fuse under the dash and also a fuse in the engine bay. I would carefully read the owners manual and look for multiple fuse locations.

Did you let a mechanic do any work under the dash? It's easy to miss one little wire that isn't part of any major system. Just tell him to put it back together.

Do the power outlets have a different fuse than the cig lighter ?

If its a factory item then it has a fuse in one of the fuse panels, under hood, under dash, on ends of dash, or even under the front or back seats. If its one someone installed then the fuse is somewhere in it's positive wire, stuffed under the dash or behind the console.

You should be able to find that information in your owners manual. If not your car should still be under factory warranty.

Check the fuses for the power outlets.They are separate than the cigar outlet.They are located under the back rear seat on the drivers side.It will be fuse number 46 for power outlet 1 and 15 for outlet 2.Hope this helps.Good luck.

Check fuses located at driver's left dash area and under the hood.

Have you checked the fuse box under the rear LH side chair?? This is where the fuses for the outlets are. Hopefully this helps

look under the drivers rear seat for the rear fuse block it will be under a black box right there

Replace the Aux Pwr fuse. On the 2008 Equinox, this fuse is in the fuse block under the hood. It is fuse number 3, 20A (yellow), located on the left side as you're looking it, in the slot immediately forward of the fuse puller tool. Way too late for Kevin256, but I just did this on my daughter's '08 Equinox and it fixed the problem.