why does dc amperage change if I install the power supply up-side down
Why must current drop if heat rises? This has to do with Arrhenius Effect of with MTBF reducing 50% for each 10'C junction rise in semiconductors. Orientation of convection flow on the hottest parts could have this effect to optimize the chimney effect in one direction.  Convection Air flow has a significant effect the thermal resistance in deg C/ Watt. In this case 40% is significant.