The whole reason that he is defeated is because he is weaponless, his lightsaber is lost out the window. However, this is a lie. There are two scenes that prove this is a deception by the dark lord of the sith.
When Palpatine tried unleashing Force lightning on Windu (who was blocking it), Palpatine was tapping really deep into the dark side. Windu was basically using a special technique that took used Palpatine's connection to the dark side to his (Windu's) own advantage. Palpatine wasn't shocking himself.
With the Jedi and Sith seeming philosophically the same to Anakin, he inevitably chose the side that at least might save his wife. Anakin dismembered Windu, allowing Palpatine to drop his façade of weakness and assault the Jedi Master with lightning once more, killing him.
With Chancellor Palpatine's death, the de facto "Prime Minister" of the Republic, the Senate would be left without a leader and there would be considerable political confusion and chaos. There would be a need to elect a new chancellor to lead the democratic government.
The showdown on Coruscant was a confrontation that took place in the Supreme Chancellor's Suite of the Galactic Senate in 19 BBY. It began after Jedi Knight Anakin Skywalker informed Master Mace Windu that Supreme Chancellor Palpatine had revealed his identity as a Sith Lord to him.
1 Darth Sidious
There has been no Sith, as powerful, meticulous, nor as evil as the Emperor himself, Darth Sidious. As previously mentioned, Sidious trained in the Dark Side by Darth Plagueis before Sidious killed Plagueis in his sleep, making Sidious a Sith Master.
As powerful as Darth Sidious may have been, it's easy to forget he actually seemed afraid of Master Yoda. As seen in Revenge of the Sith, Palpatine initially thought he could deal with the aged Jedi Master - and then, when Yoda proved able to counter the Sith Lord's Force lightning, he fled.
Conclusion: Yoda wasn't able to defeat Palpatine - or fare as well against him as Windu did - because of a number of factors: His age and physical infirmity, relative to Palpatine and Windu. His outlook on the use of the Force, which led him to reject overt aggression and hostility.
Like all in the Order, the young Korun boy was taught by Grand Master Yoda when he was a learner, and eventually went on to become a Padawan to another Jedi. At one point during his apprenticeship, Windu trained under Master T'ra Saa.
The arrest of Darth Sidious in Star Wars: Episode III - Revenge of the Sith did not go to plan, but it may have if Yoda had remained on Coruscant.
Jedi Master Yoda is the most powerful of them all. This should come as no surprise, as he was the head of the Jedi Order in the prequels and was revered for his abilities during the original trilogy. Yoda's power is unmatched and was a real threat to Darth Vader and the Imperials.
DARK SIDE FRIDAY - Did you know Palpatine feared Qui-Gon Jinn? Palpatine was immensely powerful and he could see the future which made him very confident about pretty much anyone who stood against him. So why Qui-Gon Jinn?
The reason why Qui-Gon Jinn is the most powerful Jedi in the galaxy is because he had seen everything that would unfold throughout the Skywalker Saga in a vision of the future, sacrificing himself to ensure the fulfilling of the Chosen One prophecy.
Darth Sidious, publicly known as Sheev Palpatine from Naboo, became the Dark Lord of The Sith after betraying and murdering his Sith Master Darth Plagueis. Sidious was the Dark Lord of the Sith during the last years of the Republic and the rise of the Galactic Empire.
If Qui-Gon had survived his fight against Darth Maul, he would have sensed Palpatine's evil, and Anakin wouldn't have become Darth Vader. Thus, while Qui-Gon was less powerful than Yoda, Palpatine feared him more.
Yoda was most likely the wiser of the two, but the deciding factor comes in the form of Windu's fight against the outed Sith Lord Darth Sidious in Revenge of the Sith.
Darth Maul died during a final battle with Obi-Wan in the Rebels TV series, and Palpatine couldn't have cared less. For him, finding and killing Maul for his failure simply wasn't worth the effort.
Obi-Wan Kenobi
Through it all, Obi-Wan reveals himself to be one of the very best examples of what a Jedi Knight should be: selfless, kind, and willing to do whatever it takes to protect those in need.
If Rey struck him down, Palpatine's spirit would pass into her, allowing the Sith to be reborn. Rey resisted him with the help of Ben, who'd returned to the light. But their defiance gave Sidious a new opportunity – he would drain the energy of their Force dyad to restore his own body, then rule alone.
Darth Sidious was able to cheat his upcoming death by transferring his spirit into a clone body while falling into the reactor core of the second Death Star. He later sought to prolong his existence by futilely manipulating his grandchild Rey into killing him so he could live further by possessing her body.