stacking power supplies?

Of course it is always preferable to place each individual component on its own shelf. But for reasons of domestic tranquility I may need to limit myself to one taller rack rather than two shorter ones. Shelves will be at a premium.

One option I have is to place a Supercap, XPS, and tuner power supply stacked on top of one another on the bottom-most shelf (the opening is large enough). Has anyone tried such an arrangement? Are there clearly audible drawbacks? If so, how do they manifest themselves?

I once stacked a pair of 135s, with no problems that I could detect. I don't know how power supplies will behave in a similar situation.