There was a reason the Emperor kept certain Sith relics in his office in the Star Wars prequel trilogy. The Jedi had believed the Sith extinct for millennia. In reality, after the defeat of Darth Bane, the Sith retreated into the shadows, recuperating and playing the long game. Their plans came to a head in Palpatine, the secret Sith Lord who became Chancellor of the Republic and even stood side-by-side with Jedi Masters without their recognizing his presence as a Sith.
Curiously, for all he was trying to keep his identity a secret, Star Wars: Episode III - Revenge of the Sith, he still didn't realize he was entering a Sith Lord's lair, where his power was at its greatest.
E.K. Johnston's novel Queen's Hope reveals there was a reason Palpatine kept certain relics in his office, though - to absorb his Force Lightning when his anger could not be contained any longer. Sith are fueled by anger and hatred, and occasionally those emotions would get to be too much for Palpatine. To remedy it, he would slip away into his office and blast away at relics designed to absorb the power of the dark side. The book hints there's an almost cathartic sense of release associated with using Force Lightning, meaning this allowed Palpatine to vent his anger and regain his self-control before he slipped and unwittingly allowed the Jedi to sense his true nature.
According to Claudia Gray's novel The High Republic: Into The Dark, there are three types of Force artifacts; some contain memories or even the spirits of Force s, some enhance a Jedi or Sith's ability to use the Force, and some hinder or confound that ability. At least some of the relics in Palpatine's office were presumably variants of the third type of Force artifact, designed to absorb the dark side into themselves. It's possible Palpatine could then choose to tap into the power stored there to amplify his own abilities should he need a boost at some point.
It's fascinating to see how Palpatine handled being around the Jedi for so long, undetected all the while. For all the Sith like Palpatine are good at hiding, the nature of the dark side lends itself to violence, meaning he would have been constantly battling to restrain his own desire to destroy. No doubt some of Palpatine's political schemes were hatched out of pure vindictiveness, allowing him another way to vent his frustration at denying himself. Ultimately, though, the time came when Palpatine no longer had to hide - and when that moment came, he was able to proudly display those Sith relics as the Star Wars saga entered its darkest time.
