Is PoE more efficient than plugging in adapters for each network device?
And at what scale does it start to matter?
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From my perspective; I’m going for a 3 node mesh router, plus 2 switches, and was considering if in 5 years time the electricity difference would be less than the extra upfront cost. The absolute max length of cable would probably be around 30m
Converting power once vs X times definitely has an efficiency factor.
Really depends. If you have 1 device that uses 10W with 90% efficiency, you lose 1 W. If you have 10, 1W devices with 90% efficiency, you lose 1 watt.
It is less efficient if X device has lower efficiency or if you have DC/DC converters in series (which is likely with PoE), but likely it is negligable difference.