which ebooks vendors are compatible with calibre?

[king of nowhere]

Well, pretty much what it says in the title. I can find a list of calibre-compatible formats, but most vendors are not specifying the format until after you buy the ebook. Also, I have no idea if some of them put in some anti-piracy protections that make it only readable by their specific program.

I just want to be sure I can read my ebook; I once had troubles opening one, and since then I've been super suspicious

[Ripheus23]

I'm sorry I can't help actually answer your question, but I do have to note that I first thought the thread's title was "which ebook vendors are edible"

[Undead Wookiee]

Well kindle devices use .mobi, and you can convert doc, pdf, epub and several others as well. I can't remember what all is available but you can easily just install and fire it up to see what your options are.