Dave Plowman wrote:

On the PC desktop here (Gigabyte MB) the USB power is on at all times the
PC is plugged into the mains. The separate web cam has a couple of LED
indicators. I assume this is under BIOS control, but can't find a setting.
But then the BIOS uses all sort of acronyms I don't understand.

Any easy way of disabling this? So USB power only comes on when I boot the
PC?

maybe a BIOS/UEFI setting, but more likely windows.

a USB device (e.g. keyboard/mouse) may wake the computer from sleep, so
the USB controller and root hub (EHCI/XHCI etc) may be kept powered-up
to allow that, within device manager you should see "power management"
tabs all the way down the USB device tree, where you can tell windows if
specific devices are allowed to bring the computer out of sleep, or can
be powered-off.

Sometimes these tabs go AWOL.