The energy conservation law is compatible with every single observation we have made inside the Milky Way in science, or outside science, so the empirical evidence in favor of it is overwhelming, diverse, and universal.
Theoretically, the case is also clear. Emmy Noether demonstrated that conservation laws are linked to symmetries. The validity of the energy conservation law is equivalent to the time-translational symmetry of the laws of physics: the same phenomena occur if one starts with the same initial conditions but just a bit later. This is true for the laws of mechanics, field theory, electromagnetism, nuclear interactions, classical physics, quantum mechanics, thermodynamics and statistical physics, special relativity. The energy conservation law is valid in all these situations and respected by all the major theories describing these subfields of physics.
Motors, those produced by Faraday, Tesla, or anyone else, as well as all other engines and objects in the Universe preserve the energy, too. And there exists no equivalence or analogy between the energy conservation law and the existence of Tesla's or Faraday's motor. In particular, there has never existed any solid evidence – empirical or theoretical – that electricity or magnetism couldn't do work. So any analogy between these totally different questions is an example of something technically referred to as demagogy. To create legitimate doubts about the validity of such an important and well-established law, one would need an observation or an arguments that actually discusses the technical properties of energy (and one would probably have to construct a viable theory disagreeing with the energy conservation law that is compatible with the observations) – rather than demagogic comparisons to completely different questions that the speaker desires to be answered by the same answer No although there doesn't exist a glimpse of a rational reason why the answers should be the same.
To see violations of the energy conservation law, one has to go to cosmology. However, due to the slow evolution of the Universe today, one needs to wait approximately for 10 billion years for the total energy of a system to change by an amount comparable to 100%. In the early stages of the cosmological evolution of our Universe, the total energy wasn't conserved – this is particularly important for cosmic inflation that created the energy of the whole Cosmos out of "almost nothing". But this non-conservation depended on the background spacetime's heavy violation of the time-translational symmetry.