Just an additional note from someone who read every Expanded Universe book there is before Disney's version and even Episode 1-3 came out.
Jedi are ultimately pacifists. If during a fight a sith surrenders a Jedi will stop fighting and arrest them and even better rehabilitate them back into a Jedi especially if they were a Jedi to begin with.
Jedi don't use certain force powers because of the powers destructive nature. This is the case with force lightening. Palpatine is not the only one who can channel the force to produce electric current. Some Jedi can't do force lightening because they access the force in a different way. For example some Jedi don't have telekinetic abilities. Some Jedi can only do force lightening because their species can actually manipulate energy better or actually produce electrical current on their own, such was the case with Jedi Master Arca Jeth. In general though Jedi stray away from powers that cause suffering and destruction (remember suffering leads to the dark side).
So Jedi are pacifists, and they don't use destructive powers. And now it all comes down to why. Jedi get their powers from the force. The force is literally the life energy of the universe. When Alderaan was destroyed the Jedi were weakened (as were the sith) because of all the loss of life. To kill only goes against the force and weakens one's own powers. This is why the sith are perverted. Every time the sith kill on the scale of planets they actually weaken themselves and this is why the Jedi will always be stronger - in part because jedi are accustomed to fighting without abusing the power of the force, they channel what they need (sort of like superman) they do not give into anger and they do not let the force flow erratically through them like a dam breaking. Hence, Jedi know self control - and sith do not.
Sith are temporarily stronger because the dark side allows them to channel more force at once but they are dependent on the force after, and if put in a situation were their power was drained, or alternatively where they channeled more power than they could handle at once, they wouldn't be able to compensate or adapt as well as a Jedi would. Because Sith are so dependent on the force they also burn out and shrivel up like a prune like Palpatine.
Palpatine wasn't that way from being old, he was that way from using extensive power to hide himself among other things. Which is why he started cloning himself to compensate for his failing body. More importantly Sith usually number in the one or two's and Jedi are often in the ten's to hundreds. Just a handful of Jedi together can amplify their power to throw star destroyers across the galaxy (something 1 or 2 sith could never do), or they could even maintain a temporary force barrier that protects a whole planet from an armada in space.
This is why its borderline ridiculous in the prequels that jedi council members could not maintain a force barrier against a droid army. Unless their powers were somehow being dampened by a powerful Sith Lord, then a handful of Jedi together like that is nearly unstoppable.