And this is likely not the only one the NSA has :) It’s very easy to tap pretty much any electrical bus these days which uses a cable the tap itself can be very basic as it’s completely passive.

I’ve seen a demonstration of similar taps on VGA cables that transmit the entire image to a remove reciecer which is often implanted near by in a power socket, light fixture or anything else where you have a reliable power supply and enough wires to hide and even transmit a signal out side over the power lines.