The USB expansion cards derive power from the PCI or PCI Express slot on the motherboard. When high-powered USB devices are connected to the USB expansion card, the power provided by the slot may not be enough to power all of the devices and you should connect additional sources of power. When you troubleshoot issues, you should connect an additional source of power.
Symptoms that you are experiencing power-related issues include certain devices not working correctly, not all of the devices working at the same time, and certain devices not working at all.
Examples of low-powered USB devices include USB mice, keyboards, and flash drives. An example of a high-powered USB device is an external hard drive that does not have an external source of power.