Take a modern setting and a character with a good working knowledge of physics and no fear on telling people about whatever supernatural stuff they've found. As the only piece of magic in the setting, suppose that they are given a large branch of wood that burns eternally and produces smokeless but hot fire. Suppose also that this branch's fire can't start other eternal fires, but can start normal ones.
Clearly, this is a source of infinite energy. However, the power is very low. Leaving aside the social implications of discovering what appears to be magic, can something as small as this have world-changing consequences? On one hand, "infinite energy" is setting off alarm bells for me, but on the other, I have no idea how to change the world with something that would take an hour to heat up my bathtub. Am I overestimating the dangers of including such an object?