I don't believe that's the way it has ever worked. The specs limit how much current a device can draw and under what circumstances. They say very little about what the USB host or hub is required to supply.[No, that's not the way it works.Even at 12w Peak for a Pi5, that should still leave 33w for everything else, no?
Last time I looked at the (partial) spec for USB 2, bus powered devices were supposed to draw no more than 100mA until after enumeration and the host had confirmed that it could supply more (up to 500mA). I've not checked the USB 3 specs but I'd expect that to be the same bar the upper limit.
USB C introduced USB PD which changed everything.
My experience these days though is that a lot of USB hosts and devices (USB C and various "fast charge" standards excepted) don't stick to the spec. Hosts will supply as much current as the device wants (subject to an often unspecified upper limit), devices will try to draw as much as they want from the beginning.
Statistics: Posted by thagrol — Thu Jan 25, 2024 1:44 am