It depends on the kind of supernova. Type Ia[1] is really insane. 10^44 J is a thing, that I think can blind you, even you've chosen a spot for your picnic to watch a Big Boom at distance of 1 parsec. A white dwarf made mostly of carbon burns all the carbon into oxygen in matter of seconds, and then it burns some of oxygen that was a result of burning carbon. It would like to continue brewing more and more heavy elements, but can't, because it becomes so hot, that gravity is no longer enough to keep the matter from flying away.

[1] https://en.wikipedia.org/wiki/Type_Ia_supernova