How much is down to conflict between power supply designer and EMC
compliance bod?
Designer: I want convection vent holes here, here and here, through the
shielding
EMC bod: No way, I can let you have a few holes here and thats your lot

Just repaired an LCD monitor, probably started failure with ESR'd caps then
ohmic zener and eventually blown backlight inverter pair of transistors and
blown fuse. Plenty of holes top, side and bottom of the shield on the
digital processing side but only holes at the top on the ps side. So air
comes in on the colder side at bottom rises to the top by about mid board
and little or no air traversing the hottest section, that whole section in a
dead-zone in more ways than one, brilliant