Let me make this clear- Robert Browning did write a poem entitled The Pied Piper of Hamelin, which has an epilogue about Transylvania. In fact it was about the Saxons of Transylvania. he did not write the novel Dracula.
The person who did was Bram Stoker, who wrote this novel in and around the time of the novel Frankenstein. Still, it was based upon a man by the name of Tepes... with a few plays at creative writing. Both were published and both were successes.
Note: Bram Stoker wrote Dracula... not Robert Browning.