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I have a lot of issues with too little current being supplied by my motherboard's USB ports.
My USB 3.0 ports clearly don't provide 900mA each. And my USB 2.0 ports clearly don't provide 500mA each.

If I only connect one device at a time though, I have no power issues with that device.

So I assume that some of my USB ports are connected to the same power supply source, forcing multiple USB ports to use the same current pool or whatever you wanna call it.

How can I find out which USB ports are internally connected to the same power source?

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It is very likely that ALL your USB ports are connected to the same source on your mainboard. It is a typical practice to provide the USB VBUS power directly from +5VStandby voltage rail, which is provided directly from the PSU of your PC box. This is done primarily for the purpose to have wake-up capabilities from keyboard or mouse, when the PC is in standby (sleep/hibernate) mode. Different PSUs provide different load capacity on the +5VSB rail. I am just looking at Zalman 600W PSU, and it says Max Load of only 2.5A on +5VSB rail, which is the minimum by AT12V PSU specifications. Smaller older PSUs can have as low as 0.8A of load on 5VSB. Clearly this is not much.

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  • But I'm pretty sure that they are not all connected because in some configurations my devices receive enough current and in some configurations they don't.
    – Forivin
    Commented Aug 11, 2016 at 8:24

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