How to Read a Power-Supply Datasheet: The Numbers That Matter

A power-supply datasheet packs a lot into two pages. Here is a quick tour of the figures that actually decide whether a part fits your design.

Input voltage range

Look for a universal input (typically 85–264 VAC) if the product ships internationally. A narrower range may be cheaper but ties you to one region. Check the frequency too (50/60 Hz) and whether there is an inrush-current figure you need to design around.

Output - and the derating curve

The headline wattage is the figure at 25°C with good airflow. The number that matters in the real world is the derating curve: most supplies must shed output as ambient temperature rises or if convection-cooled. A "200 W" unit may only be good for 140 W at 50°C with no fan. Always size against the curve, not the headline.

Efficiency and no-load draw

Higher efficiency (90–95%+ is common now) means less heat to get rid of and a smaller thermal budget. If the product spends a lot of time idle, also check the no-load / standby consumption.

Hold-up time

Hold-up is how long the output stays in regulation after the mains is removed - typically 10–20 ms. It matters if your equipment must ride through brief dropouts or sequence a clean shutdown.

Protections

Look for OVP (over-voltage), OCP / OLP (over-current / overload), OTP (over-temperature) and SCP (short-circuit). Note the recovery behaviour - auto-recovery versus a power-cycle latch - because it changes how your system behaves after a fault.

Isolation and approvals

Check the isolation voltage (e.g. 3 kVAC input-to-output) and, critically, the safety approvals for your market and application: IEC/EN/UL 62368-1 for general ITE/AV, IEC 60601-1 for medical, plus EMC marks such as EN 55032. The right certificate on the sheet can save weeks of compliance work later.

Every product on our site lists its key specs and links the manufacturer datasheet. Not sure which part fits? Send us the requirement and we will shortlist the options.