How to read a derating curve?

In MEAN WELL’s specification you can find 2 derating curves, in below example the 300W open frame power supply: EPP-300

1. The Derating Curve with the Ambient Temperature vs. Load
2. The Derating Curve with the Input Voltage vs. Load

3. In this Curve one can find that the maximum load of this power supply is 300W at 50dC when an external air flow of 20.5CFM is applied. For temperatures exceeding 50dC, 60dC for example additional derating need to be applied, in above case at 60dC the maximum load would be 225W. (50dC 300W, 70dC 150W => from 50dC to 60dC:  75W derating)

4. In case this power supply would be used at 90VAC input, a derating of 80% must be applied. So, in previous example with the 20.5CFM forced air the max load would be 240W. In case of an ambient temperature of 60dC and a 90VAC input the maximum rated power would be 225W * 0.8 = 180W with 20.5CFM forced air.

5. If the power supply is used in an application without additional forced Air, the power supply will be derated to 200W till a maximum temperature of 50dC
6. In case it will be powered by a 90VAC input the power supply has to be additionally derated to 80% of the 200W = 160W max