One of the most fascinating aspects of Einstein's general theory of relativity (GR) is the uncanny correspondence of the black hole mechanics and thermodynamics. From this, it follows that up to 29% of the total energy of a black hole can be extracted, which is the measure of black hole's rotational energy. For typical supermassive black holes located at the centres of most of galaxies, the available energy is of order of 10^74 eV, making them the largest energy reservoirs in the Universe. It is therefore most pertinent to tap this enormous source most effectively and ultra efficiently. In this talk, I will review the leading mechanisms of the black hole energy extraction, focusing in detail on the novel, ultra-efficient regime of the magnetic Penrose process and an extraordinary mechanism of the energy gain by a charged particle emitting synchrotron radiation. Comparing theoretical results with the relevant multi-messenger observational data, I will show that described mechanisms could indeed foot the bill for powering engines of such astrophysical phenomena as ultra-high-energy cosmic rays and relativistic jets.