The novel implies that essence transfer was something that Plagueis had discovered/invented, and passed on to Palpatine alone:
Palpatine's very own apprentice had turned against him, the way he himself had turned against Plagueis...whose secret to immortality he had stolen. Plagueis had not acted fast enough in his own moment of death. But Sidious, sensing the flickering light in his apprentice, had been ready for years.[...]
The transfer was imperfect, and the cloned body wasn't enough. Perhaps Plagueis was having the last laugh after all. Maybe his secret remained secret.
But the novel also makes it clear that Palpatine was indeed channeling the power of every Sith before him...
Palpatine raised his perfect, healed hands, and called on all the dark power of the Force and the Sith who had come before him, and pulled their life from their very bodies.
A scavenger girl is no match for the power in me. I am all the Sith!
And it was through that eventual union, unexpected as it was, that Rey was born. The perfect vessel. Strong enough to contain all the power of the Sith.
However, it does not tell us *how* he managed to accumulate said power.