How to fix the "Unknown USB device needs more power than the Port can Supply" error?

There's a message popping up saying:

Unknown USB device needs more power than the Port can Supply.

What do I have to do? What's wrong?

This message usually appears when a system uses a certified bus-powered USB hub (hub power and power for all it's ports are coming from a single upstream cable from host). In this case the system knows (via hub descriptors) that this is bus-powered hub, and therefore it must have the natural limits of how much power can be theoretically taken from upstream, and delivered to downstream ports.

Therefore the bus-powered hubs are allowed to allocate only a fraction of power that is normally available from normal ports (500 or 900 mA) and from self-powered hubs (powered from external AC-DC adapters). To prevent the hub upstream port (host downstream) from overloading, USB has a two-step mechanism.

First step is an informative. USB devices must take only 100/150 mA from VBUS to respond with device descriptors. The device descriptor(s) have an information on how much current it is expecting to use under full-functional mode, its maximum. The system reads this information, and, knowing whether the hub can or can't (theoretically) supply this power, it may or may not proceed with final step of device configuration, SET_CONFIG(). If the system determines that the port does have enough power, it finishes the enumeration. If this is a bus-powered hub (100 mA per port), and device declares the use of 500 mA, the system won't proceed with configuration and will display the warning message. Thus the device will be rejected. Whether the device really consumes that current remains however unknown.

In fact, in USB 2.0 power management schema of things, the "high-power" device will not be admitted even if other ports don't have anything plugged in, and theoretically the hub might have enough resource to power it up. This is a major inconvenience from user standpoint. To avoid this inconvenience, USB industry has invented illegal "semi-self-powered" hubs, tyhe hubs who can be bus-powered, but don't report this in their descriptors, fooling the host system into thinking that this is a normal self-powered hub, so no restrictions will be imposed. The rest is up to user's lack or luck thereof.

So, it looks like you have a misfortune (or fortune) to have a certified USB hub that plays nicely, in accord with USB specifications. To avoid this messages either use a self-powered hub, or use the bootleg hubs that don't report their bus-powered status, and pray that the host port has enough power to drive whatever devices you are plugging into the hub without losing much of VBUS voltage level.

If there are no USB devices plugged in and you're still getting that message, something might be short-circuiting one of your USB ports. Carefully check all the ports.

A possible cause might be one of the metal anti-RFI "fingers" in the I/O shield plate accidentally getting inside an USB port when installing the motherboard. Normally these "fingers" should only contact the metal shells of the connectors on the motherboard: they should never go inside the actual connector.