Quote from: vertigo on May 11, 2021, 19:52:46
I was thinking more along the lines of a laptop passing power through from AC to the monitor, i.e. powering a monitor when the laptop is plugged in. But also for desktops, to be able to have just one cord going from the desktop to the monitor for everything. An example use case for either situation, and something I've wanted to do before, is to get a touchscreen monitor and have it connected via one USB cable to provide poewr, video, and USB, so it could be used as a tethered tablet. This would be great for using a computer while in bed or on the couch.
a) It would take up two ports on the laptop (one for a display and one for a power supply). Not necessarily a deal-breaker, but worth mentioning.
b) Laptop's power supply would have to be sized to accommodate a monitor. Making it bigger, heavier and more expensive.
c) The connector used for power supply would have to be able to carry enough power for both a laptop and a monitor. USB PD is not there - officially, it tops out at 100 W which is plenty for ultrabooks. But not enough for an ultrabook plus a desktop monitor.
d) And when it comes to power, it's not just a monitor, but also all the peripherals connected to it.
I can't see an advantage compared to the other way around where a monitor essentially acts as a power supply. So, a desktop monitor is permanently connected to the grid, potentially also a wired computer network, speakers, camera, whatever, powering all that. And by connecting a single cable, you get both power for a laptop and data, all the peripherals. Thunderbolt is superior for this but USB can work for anything that can be made as a USB device. You take up only one port on a laptop and you can keep a charger in a bag.
Yes, USB4 can be used to connect e.g. a drawing tablet to a desktop with a single cable. Assuming it can fit within a 100 W budget. But your computer has to be able to supply that much power on an USB port. Technically, USB allows it. But the motherboard manufacturer has to implement it. And similarly, tablet's manufacturer has to build it so it supports USB PD. The thing here is that they can't assume a computer will be able to supply enough power so there has to be an alternate means of powering it and so they might not bother with USB PD on the video/ data port at all (especially if only a few computers can supply enough power). If it's USB4, I think USB + video on one cable is given. The potential complication here is that USB-C is not that common on desktops and that they will probably want backward compatibility and some flexibility. Another complication is that video output on a desktop is often on a video card. You have to get video and USB on the same port, not to mention PCIe for Thunderbolt. This is easier in a laptop with its higher integration.