Truth about Palpatine
OK, Plageus was Palpatines apprentice and Palpatine had killed him in his sleep. Plageus had taught Palpatine everything about the force including how to prevent death, ironicallly everyone but himself. Palpatine knows about how to prevent death but does not know how to actually acheive it. He needs Anakin's help in order to acheive it. Therefore he never lied to Anakin about being able to save Padme.
Now, when Padme died, Palpatine nor Vader knew that she survived to have kids and it was kept a secret between Obiwan and Yoda. In the orginal trilogy Obi wan says, "if Palpatine knew if Anakin were to have any offspring, they would be a threat to him". So, Palpatine not knowing about the kids and that she survived is verified.
After she died Anakin didn't care about learning how to prevent death from then on. So, it must be impossible to bring someone back from the dead after they died, otherwise Anakin would try to learn it through the darkside. So, only to prevent death is possible. Palpatine got his way regardless if she survived or didn't.
This is what I can actually understand what happens, it open to others...