One problem that sometimes arises when using embedded single board computers like the Raspberry Pi is that they often cannot provide enough current to power devices through the USB port.
Over on YouTube user KD9 BVO wanted to use his RTL-SDR with a Raspberry Pi, but found that the Raspberry Pi shut down whenever he plugged it in, due to it using too much current. To get around this problem he decided to build a DIY powered USB hub. This solution allows the RTL-SDR to be powered via the hub itself, rather than through the Raspberry Pi USB port.
In the video he takes an existing unpowered hub and shows how to modify it to provide power directly to the RTL-SDR via an external power supply.