Yes, for power supplies certified >2000m please read the “note” in the spec.
In general, for unpotted models, a derating of 5°C/1000m has to be applied and for potted models, a derating of  3.5°C/1000m has to be applied.
For example LRS-75-24:
The datasheet shows:
The Note. 7 shows:
At 5000m the derating curve will need to move 15°C following the arrow (1)
At full load the maximum operating temperature at 5000m will be 35°C shown at (2)