In non-peak power usage environments, the power selection of Open Frame PSU is determined by the power required by the system, the temperature inside the system, and the wind flow provided by the system. 
Referring to the product specifications of FSP260-P35-A12, when the power is operating under an ambient temperature of -20℃~50℃, the output power is 260W @ 18.4 CFM; and under the condition with no wind flow, it is only 150W @ Convection. If the temperature of the PSU’s working environment exceeds 50℃, you must refer to the derating curve of the power and reduce the output power as the ambient temperature rises in order to ensure the power will not enter over-temperature protection or even get damaged from overheating. If it is a peak power usage environment, please contact our business unit to have further discussions.