Surprising behavior of Always On USB ports on a ThinkPad laptop

Unfortunately, it really depends on the specifics of the implementation of both the hub and device.

Now, the vast majority of simple hubs don't really implement any sort of power control. They'll just connect the USB power lines directly to either their host or an external (regulated) power supply, which means you'd effectively be sharing the capacity of the power source over all ports.

In practice, however, USB charging gets quite complex. The bottom line is: your USB 1.1 hub will probably charge your peripherals, but at a reduced rate. This isn't because the hub is actively limiting the current output, but because peripherals will limit the current they draw unless they can positively confirm the host is capable of supplying that current - to prevent damage to hosts that can't.

Now, this reduced rate depends on the specific peripheral, and also on the specific hub - but it likely ranges from 100 mA to 500 mA, which is far less than a modern smartphone's max over 1000 mA.

To elaborate:

• If the host implements some kind of power control, then the peripheral must initiate a data connection and negotiate properly. Even though this is technically required by spec (except the newer battery charging specs), some peripherals might not do so - I imagine most smartphones will at least try, but there's many dumber USB peripherals that won't.
  • In the case of a hub connected to a USB power supply without a proper host, it might not work at all.
  • Negotiation is as follows:
    • Each peripheral is permitted to draw one unit load without negotiation. Each peripheral should communicate with the host to request more units.
    • USB 1.1 and 2.0 define one unit load as 100 mA, with a max of 5 unit loads (500 mA).
    • USB 3.0 defines one unit load as 150 mA, with a max of 6 unit loads (900 mA).
• Modern devices often need more power - smartphones often draw 1000 mA - 2000 mA.
  • There's a battery charging specification that deals with this. See https://www.pericom.com/support/technical-articles/how-usb-charges-just-about-any-electronic-device/ for details on how its negotiation and detection works, but that's not too important.
    • The charging limit is 1500 mA, but only if the data lines are shorted together (or respond as if they have been). This is not the case with a data-capable host like a USB hub. There's an additional profile that deals with this, but a USB 1.1 hub probably does not implement it.
      • Practically, with a non-compatible host most smarter peripherals will fail to detect a high-capacity source and will therefore fall back to charging at 500 mA max. This means your USB hub will likely charge significantly slower than plugging the peripheral directly into the charger.
  • There are some other specs (e.g. Apple's protocol, Qualcomm's quick charge protocol, etc.). They all have their own detection and negotiation methods. They also will not occur with a USB 1.1 hub.
  • There's a newer USB Power Delivery spec, but it deals with all sorts of wacky things like different voltages. Again, with a USB 1.1 hub none of that applies.

I’ve not tested the MacBook. The Dell XPS 13 I have in front of me right now appears not to even trickle charge on USB-C at 29W even when the laptop is turned off ... it wants 45W. I’m going to leave it overnight but I am not confident it will work at all.