> Office equipment doesn't really have "transformers" anymore, everything uses switched-mode power supplies. The way they work, is that they have an output buffer (a capacitor or inductor) and rapidly turn a switch on and off to keep that output buffer at the right level...
Overwhelming majority of mains-powered devices does, in fact, have a transformer. It is part of a switched-mode power supply, though. The only devices that do not have one are those that are fully enclosed in plastics and user can not under any circumstances come to contact with any of the conductive parts. Typical example would be a LED light bulb or wall-socket powered WiFi repeater (without RJ45 port).
It is pretty hard to create a transformer-less device using plain rectifier/switch/capacitor topology. The biggest issues obviously are the high voltage before the switch and dead time when the mains voltage drops near zero 100 times per second. Most switch ICs made in the "west" cannot go up to 325V and are thus usually used with a transformer to step the voltage down below 60V. If you get a Chinese chip that can work off-line (as in directly with the 325V mains voltage), such as KP1063 <https://datasheet.lcsc.com/lcsc/2103171532_Kiwi-Instruments-...>, it still needs an inductor to bridge the mains dead time. This is incidentally done by the transformer in traditional power supplies. Capacitor would have to be huge to smooth over those for any significant power draw.
> If we increase the voltage across the wires to 120V and down-convert that to 12V at the computer we'd only need to conduct 1A and the wire loss would be 0.5V, which at 1A is a power loss of 0.5W. That's completely acceptable, and because the computer down-converts anyways we don't really have to care about it getting 119.5V instead of 120V either.
We could use 48V, which would bring the cable losses to about 3.3W (for those 100 ft). Or maybe instead of wiring from the mains box, we would place transformers along the wall sockets. Some new installations already do that and install charging USB ports. USB-PD is now specified up to 48V / 5A.
I think that we are already seeing devices abandoning the traditional DC connectors in favor of USB. A lot more people now have a large bank of charging USB-A and USB-C ports on their desks. Some vendors already integrate them in extension cords. It won't take long for LED lamps to come with an USB cord and an optional mains/USB transformer SMPS ("phone charger"). Laptops are already charging (and docking) via USB-C with PD, it might not take long for screens to follow.
Stepping 48V DC down to 12V, 5V, 3.3V is way easier and can actually work the way you have described above.
Overwhelming majority of mains-powered devices does, in fact, have a transformer. It is part of a switched-mode power supply, though. The only devices that do not have one are those that are fully enclosed in plastics and user can not under any circumstances come to contact with any of the conductive parts. Typical example would be a LED light bulb or wall-socket powered WiFi repeater (without RJ45 port).
It is pretty hard to create a transformer-less device using plain rectifier/switch/capacitor topology. The biggest issues obviously are the high voltage before the switch and dead time when the mains voltage drops near zero 100 times per second. Most switch ICs made in the "west" cannot go up to 325V and are thus usually used with a transformer to step the voltage down below 60V. If you get a Chinese chip that can work off-line (as in directly with the 325V mains voltage), such as KP1063 <https://datasheet.lcsc.com/lcsc/2103171532_Kiwi-Instruments-...>, it still needs an inductor to bridge the mains dead time. This is incidentally done by the transformer in traditional power supplies. Capacitor would have to be huge to smooth over those for any significant power draw.
> If we increase the voltage across the wires to 120V and down-convert that to 12V at the computer we'd only need to conduct 1A and the wire loss would be 0.5V, which at 1A is a power loss of 0.5W. That's completely acceptable, and because the computer down-converts anyways we don't really have to care about it getting 119.5V instead of 120V either.
We could use 48V, which would bring the cable losses to about 3.3W (for those 100 ft). Or maybe instead of wiring from the mains box, we would place transformers along the wall sockets. Some new installations already do that and install charging USB ports. USB-PD is now specified up to 48V / 5A.
I think that we are already seeing devices abandoning the traditional DC connectors in favor of USB. A lot more people now have a large bank of charging USB-A and USB-C ports on their desks. Some vendors already integrate them in extension cords. It won't take long for LED lamps to come with an USB cord and an optional mains/USB transformer SMPS ("phone charger"). Laptops are already charging (and docking) via USB-C with PD, it might not take long for screens to follow.
Stepping 48V DC down to 12V, 5V, 3.3V is way easier and can actually work the way you have described above.