In the Philippines, again putting it in a Western context (that is my own) a quack doctor is sort of a combination of an herbalist and what might typically be thought of as a voodoo practitioner in the Haitian, West African or New Orleans tradition.
One of the dominant differences between doctors of any type in the West and the more folkloric practitioners in the East is that in the West, if you have an illness of the body you would go to any number of different types of doctors, depending on what was wrong with you. This is also one of the reasons causing U.S. health care cost to skyrocket. If an individual had a problem mentally, they might see a psychologist or if they’re really crazy, a psychiatrist. If one is ailing in spirit, they would likely see a priest, rabbi, Reverend etc. depending on personal religious or spiritual disciplines.
In African and Asian cultures in various part of the world you have a good chance of finding a doctor who is knowledgeable in all three and how they interrelate; mind, body and spirit. This is the level a quack doctor would practice on.
They are widely consulted in the Philippines and noting some of the prices I’ve been told by friends I’d summarize the Philippines has quack doctors of both types.
You can read about a quack doctor experience here.