Supernovae, because of their great ferocity, are relatively rare events. There have only been seven supernovae in our Galaxy in all of recorded human history. They appear and then annihilate each other, returning to equilibrium. Hawking radiation involves one of these virtual particle pairs being created near the black hole's event horizon. The particle with negative energy is swallowed by the black hole, and the other escapes.
Negative energy means a reduction in energy, so the black hole loses mass.
The vast amounts of gold, uranium, and other elements with high atomic numbers on the Earth give you some idea of the size of titanic explosions that we call supernovae. Various things I've written. All rights reserved.