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.

Inrush current occurs at the moment when an electrical device is powered on. It is caused by the rapid charging of input-side stabilization and filter capacitors. The peak current is typically much higher than the normal operating current, hence referred to as inrush current. This current lasts only for a short period and disappears once the capacitors are fully charged. There is a high slope of di/dt in inrush current. Although the time is short, the rising edge of the waveform contains numerous high-frequency components which is analyzed by Fourier transform, which can cause electromagnetic interference (EMI).

Additionally, the fuse rating (I²t, where I represents current and t represents time) must not be too low to withstand the inrush current and prevent unwanted fuse blowing. In end applications such as LED lighting, when many LED are switched on simultaneously, it may shut down the main power. Countermeasures are adjusting components in PSU or turn on LED lights sequentially.

Hold-up time is the “power hold duration ,”which refers to the period during which the system can continue operating after the AC power is interrupted.
The length of this time varies depending on the circuit design, generally around 10–20 milliseconds (mS). When AC power is interrupted, the power supply relies on internal energy storage components (usually large-capacitance electrolytic capacitors) to maintain the rated output voltage. Hold-up time affects both the cost and the physical size of the power supply. The duration of this time depends on how long the system needs to process or save data after a power interruption so that operations can resume smoothly once AC power is restored. This is particularly important for information processing in commercial and financial industries, as well as for production line operations in manufacturing.

If a longer Hold-up time is required, you can refer to FSP’s Backup Power and UPS products.

For space-constrained embedded devices, priority should be given to open frame power supplies with high power density and compact footprints (such as standard 2"x3", 2"x4", or 3"x5" inches). Furthermore, adopting power supplies with high conversion efficiency (e.g., meeting 80 PLUS requirements) can effectively reduce waste heat, providing higher power output without increasing the cooling volume.

The output power of open frame power supplies is generally divided into Convection Cooled and Forced Air Cooled. If the system lacks airflow or sufficient airflow for the PSU, the design must refer to the "Derating Curve" to ensure stable operation at high temperatures without triggering over-temperature protection.

Lacking an enclosure shield, open frame PSUs highly depend on internal Cable Routing and grounding design for EMI performance. Choosing EN 55032 Class B power supplies offers more system margin than Class A. Ensure the Protected Earth and Return have good contact with the metal chassis during installation, and separate AC input lines from DC output lines to prevent electromagnetic noise coupling.

Medical power supplies must comply with the IEC 60601-1 medical safety standard, which requires higher insulation strength (2 MOPP) and lower leakage current limits compared to the IEC 62368-1 safety standard for information technology equipment.