There's a reason why you want higher voltages: to minimize losses in conduits; i.e. you can move more effectively 12W in 120V/0.1A rather than 12V/1A -- the lower current, the lower resistance.
There are no 12V standards for wiring buildings, because effectivity-wise, it make no sense. Even the above-mentioned PoE is 48-56V (56V, so it can be 48V at the other end of up to the 100m long cable). The 5-12-20V USB PD is for relatively short cables, not for something that goes around your house.
Thank you for the informative reply, Lord Patrician!
Is it straightforward to step down the voltage from PoE to something that USB-C can use? My Forest M Mims Electronics book sits unread and dusty in a box somewhere so I'm not really able to interpret the schematics google is showing me :/ (apologies for extra questions)
There are PoE-to-USBC adapters available; random pick on Amazon: https://www.amazon.com/dp/B087F4QCTR (this one is af, 5V/12W and plain USB; no at, no QC or PD. If you need that, you will surely find it).
For DYI, there are dc-to-dc convertors available. Or do you intent to build your own?
It was more for curiosity's sake, but it's really cool that there's already converters. My project is very much in the "hey it would be nice if" stage right now, but I'm on the Python track at Exercism and want some "small" projects lined up once I'm finished there.
The idea is: pull in a quick 3D sketch of a home. Place (USB-C via PoE-power?) ESP32/Pi/Other devices at specific points with very precise measurements between them. Use them to determine the exact position in 3D house-space of Bluetooth low energy beacons. Use that info to help my very ADD wife find the things she loses. (because Tiles often fail)
A lot of the code to calculate position from timings already seems to be out there so I can cargo-cult things over.
In a far-too-roundabout way, that sorta kinda answers your question.
There are no 12V standards for wiring buildings, because effectivity-wise, it make no sense. Even the above-mentioned PoE is 48-56V (56V, so it can be 48V at the other end of up to the 100m long cable). The 5-12-20V USB PD is for relatively short cables, not for something that goes around your house.
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