The JitterBug is a dual-function filter that cleans up noise in both the power and data portions of the USB interface. It performs like a line conditioner for the USB voltage bus, as well as acting as a signal filter for the USB data bus. In both cases it suppresses electrical noise that interferes with your DAC's sensitive circuitry. The JitterBug can reduce timing jitter as well, but it doesn't re-clock the digital audio stream to eliminate jitter.
Slightly smaller than the DragonFly, the JitterBug has a male USB plug on one end and a female USB port on the other. If you already own a DragonFly, the JitterBug is an easy, affordable upgrade. Simply plug JitterBug into any of your computer's available USB ports, then plug the DragonFly into JitterBug's USB port. If you're using a different USB DAC, you plug the JitterBug into an available USB port, and use a USB cable to connect the JitterBug to your DAC.