fahmid, you ask a good question. I have no answer, except to say that when I read something that strikes me as postmodern, I don't normally think of it as ethnography. I think, for example, of Michael Taussig, whose books, Wikipedia tells me include
Of these, the first,The Devil and Commodity Fetishism seems the most ethnographic but not especially post modern. The second and fourth Shamanism, Colonialism, and the Wild Man and Mimesis and Alterity, strike me as postmodern but not especially ethnographic, unless any book that incorporates bits of ethnographic detail in a mass of theoretical musings is to count as ethnography. Neither provides a full enough picture of the way of life of the people whose actions are analyzed to provide sufficient context in which to judge the local relevance of the ideas on which the author is primarily focused. I haven't read the third, The Nervous System, so I can't comment on that one.
These first musings leave with exactly the question you ask, when people say "postmodern ethnography," what exactly are the exemplars they have in mind. I do hope others pitch in and tell us.