It's elementary, my dear.
The Energy Tap is one of five alien artifacts recovered by Hank "The Mighty" Henderson on an out-Sol asteroid and identified with a hypothetical 3 billion year old interstellar vessel. Only three of the artifacts have been identified by MCS — The Energy Tap, The Conductor and The Drive.
Seized by Cat Anne and her jumper fleet in the Battle of Saturn in Shadow, The Energy Tap appears to be capable of drawing off energy from remote sources at a distance of thousands of kilometers. Observed sources have included stellar objects, combustion events, nuclear generators. Energy derived from these sources is transferred to storage or systems nearby (for instance a Renavigation tub carrying the Energy Tap in its hold) and can be used to increase speed, shielding or weapons.
This was the second alien artifact recovered by Cat Anne and the first definitive proof (that is, shared publicly) of the existence on civilization other than our own.