The explosion as Palpatine was killed
Upon the demise of a potent Sith or Dark Jedi, a discharge of dark side energy would sometimes materialize. This resulting wave of force could range from incredibly destructive, to a simple disintegration of the body.
The earliest documented instance of this phenomenon occurred in 3951 BBY, when Darth Nihilus's remains were engulfed in a small scarlet explosion of energy following his death at the hands of Meetra Surik.
In the year 3637 BB, Valkorion, the Immortal Emperor, detonated in a wave of Dark Side energy, yet his physical form remained intact.
Subsequently, in 3630 BBY, within the mind of the Outlander, Valkorion's essence erupted in a surge of Dark Side energy after the Outlander brought about his end.
Not long after Palpatine assumed the position of chancellor, Darth Plagueis unleashed a similar event when Palpatine electrocuted him after plying him with enough wine to render him unconscious. The resulting burst was so powerful that it sent ripples throughout the Force, which were felt across Coruscant. However, unlike other Sith Lords who experienced this effect, Plagueis's corpse was left behind.
In 19.5 BBY, the deaths of Nikkos Tyris and the other leaders of the Jensaarai generated a dark side burst.
In 3 BBY, Shaak Ti emitted a comparable burst after intentionally plunging into the Ancient Abyss following her defeat in a duel against Galen Marek, notable because she had never been a dark-sider. Soon after, Marek seemingly unleashed a dark side burst when he gave his life in combat against Darth Sidious, although his physical body remained (and this happened after he forsook the dark side). Six years later, Sidious discharged a massive wave of blue dark side energy after being hurled down a reactor core shaft on the second Death Star. Later on Ruusan, Jerec's body vanished after Kyle Katarn killed him. In 8 ABY, the Nightsister Ocheron released a burst of dark energy upon being decapitated by Luke Skywalker. One year later, in 9 ABY, Joruus C'baoth also emitted an energy blast after Mara Jade killed him with Leia's lightsaber, creating a large hole in the side of Mount Tantiss.
Darth Traya appears to release a dark side burst in the video game Star Wars: Knights of the Old Republic II: The Sith Lords, when the Exile throws her off of Trayus Core into a bottomless pit. It remains unclear whether this was Traya releasing Dark Side energy, or simply her body being consumed by the dark power at the core of Malachor V. However, this only transpires in the dark side ending of the game, rendering it non-canonical.
Despite Jedi Master Shaak Ti never practicing the Dark Side, her death in the Sarlacc pit bore a striking resemblance to the dark side burst, possibly suggesting that the phenomenon is triggered by the Force user's power level rather than their alignment.