1 does that fan blow in or out? i assume its blowing in because theres no fan on the heatsink?...
2 do u have a fan in the front of ur case?..
im starting to believe that the psu will get enough airflow to keep it cool, due to the fact that on any given computer the hot air off the heatsink gets sucked up by the psu fan up top, so im starting to believe that since ur hot air gets blown out the back that enough air will get through to that bottom psu fan (with the green thing on)