The EFIE Device (and the kit) are designed to deliver less than 500 mV (0.5 Volt)
It’s easy to test, just hook the red and black to positive and negative respectively (12 VDC) and measure the voltage across the white and green.
I am a mechanic and the original inventor of the EFIE Technology. I specifically designed it to NOT possibly damage any computer.
But the real proof is in experience. I’ve sold many thousands of them since 1991 with ZERO computers damaged.