A plasma bomb is an explosive device which has been used by various races and cultures across the galaxy. The explosive capacity of a plasma bomb is not known, however multiple bombs are extremely destructive and have been known to render a planet uninhabitable.
In 1746, the Turei used plasma bombs to annihilate the Vaadwaur in the Delta Quadrant. Billions of Vaadwaur were killed and a nuclear winter began to rage on the planet. However, some Vaadwaur managed to survive long enought to enters stasis, and were later rescued by the USS Voyager in 2376. (VOY episode: "Dragon's Teeth")