The Start-Up Assistance is a molded board which is integrated in the cable. It is used to support the Hawk Thunder machine for 3rd party power units such as Eikon and Critical. With the help of the start-up cable the Thunder runs on 4-5 volts. The Spirit in comparison starts on 9-10 volts.
The new generation PU1 and PU2 Hawk Power Supplies are outfitted with this on the device, thus cable is not required. If your Power Supply has a boost feature, like Critical Power Supplies, the Startup Cable is not needed.