You can take power from any port there on PC. As many ports are power separate hardware like USB device and hard disk. When with USB port you can add power to attached device in two ways. From power connection with wall outlet and by leaving smaller device attached directly with USB port. Many devices take complete charge from USB port.

Instructions

o Connect power cable to power port on hardware you like to attach to USB port.

o Attach other end of power cable to power wall outlet to add power to USB device.

o Attach USB device to any USB port. If you use iPod, or USB rechargeable batteries you can charge device from USB port.

o Power down attached device if it has power switch. This raises speed of power charge.