I am looking for a word to describe people that proclaim that they possess healing powers or know remedies to cure incurable conditions or even to poses spiritual powers. A general term would be a charlatan but I want something specific. Something like the word alchemist compared to a chemist. Few words, I can think of are fake shaman, fake healers, plastic shaman, voodoo priest.
If you are talking medicine (including pseudo-scientific medicine) then you want either quack or snake-oil salesman.
Quack (MW, noun definitions 1 & 2)
a pretender to medical skill
any of various substances or mixtures sold (as by a traveling medicine show) as medicine usually without regard to their medical worth or properties
Snake-oil salesman (Cambridge)
someone who deceives people in order to get money from them
"Quack" is the most common term I know of. Occasionally, it can be used as a derogatory term for any medical doctor
If you want something a bit more verbose/proper, use the original term "Quacksalver"
c 1570, from Dutch kwakzalver (“hawker of salve”), from Middle Dutch quacken (“to brag, boast; to croak”)
i.e. Someone who boasts about the potency of their remedies, but is in fact a fraud.