Hi!

I've never had a problem turning a computer power supply upside down...the
units I've used are often free of a case and put in any direction that will
fit. Fan cooled units should not be bothered by direction or orientation of
mounting. Just don't block the fan or inlet vents.

Convection cooled units may be a bit more sensitive to orientation and
mounting direction...the wrong way could put the heat on the circuit board
and components. Depending upon how hot the supply runs this may or may not
be an issue. Of course you could always add a fan to these units.

William