How to know practical efficiency of power supply

I’m worrying in comparing practical efficiency of off board power supplies.
Each products promote maximum efficiency “95%, 96.5%” in very ideal senarios.
Does anyone recommend which part of specification should be compare to avoid mis-choice of product?

Hello uspmatitude4,

Welcome to the DigiKey community.

That is not an easy question as the answer is system dependent. It’s also a moving target as the dynamics will change as the input voltage changes along with changes in your load.

From a practical perspective, selecting a power supply with a stated 95% is identical to the 96.5%. Both efficiencies will be swamped by the previously mentioned system dependencies. For example, the powers supply should be chosen to survive sustained operation in a worst-case situation. The resulting power supply will likely be oversized thereby reducing the efficiency in the typical lightly loaded condition. It’s even paradoxically possible for the “more efficient” supply will be less efficient in this situation.

Best Wishes,