The conditions that you expect the AC-DC power supply to operate under can greatly affect the output power available. For instance, if the supply voltage is at the lower end of the specified operating range the output power may need to be de-rated. Likewise, if the temperature will be at the upper end of the specified range, then it may be required to de-rate the output power. When selecting an AC-DC power supply the headline power rating may not tell the full story, the datasheet should always be consulted to ascertain the true specification, particularly when the operating conditions are at the upper or lower extremes. All XP Power products have comprehensive datasheets available, with de-rating information to assist in determining the most appropriate power supply for any given application.