Will double-track shelving work for a computer desk?
Put your computer on the floor, where it belongs. Same with the UPS. This opens up your desk space and muffles the noise.  

The weight of LCD monitors and a printer won't be as much of a strain.

The strength of a shelf like this will depend a lot on how you attach it to the wall. Anchors in drywall hold a lot, but when they fail they leave an ugly hole and a big mess. Screwing directly in to a stud helps. Also, the track, the more the load appears as a vertical force, instead of a force trying pull the screw out of the wall. That's more reliable.

If you're not sure if your setup is strong enough, one way to approach the problem is to underbuild it, test it, then add on. So, you could put up a single track and load it with the full weight of the desk and equipment. If it holds, then put in the second rack, more screws, etc.