Kronos

"Kronos" is about a robot emissary (which Earth scientists name Kronos), sent by aliens to Earth. It lands on the coast of Mexico and goes on a rampage. The aliens have exhausted energy supplies on their own planet (which it is correctly noted may well happen here before too long), and so they sent Kronos to Earth to suck up energy from our remaining energy resources. Unknowingly, Earth counterattacks with weapons like an H-bomb, but Kronos greedily absorbs all that energy and just gets stronger and hungrier for more.

At this point, you just have to put aside the immediate obvious objection that there is far more energy in any star in the galaxy than in all the power plants on Earth, and the aliens should have just harvested energy from them.

If you can forget all that, what is left is an enjoyable typical 1950's B-movie, with what I consider to be some decent special effects for the time (except for the obvious cartoon animations of Kronos' march). Jeff Morrow, one of the better B-movie actors, delivers a decent performance as a scientist. Despite its low budget, the movie tries hard to be an early techno-thriller, replete with what was state-of-the-art technology for its time--B-47 jet bombers, missiles with nuclear warheads, computers, etc. And that also makes it a cut above the usual sci-fi B-movie of the 1950's.