Seems like there's no shortage of Real World examples of 'Funny Money', but in this instance, it led to the beginning of the end of Zaire's Mobuto Sese Seko.
Seems like in the 1990s, he attempted to pay soldiers in his army in newly minted 5 Million Zaire notes (reportedly worth US$2 at the time). The shopkeepers in the capitol refused to accept the new 5 million Zaire bill and the soldiers mutinied.
http://articles.latimes.com/1993-02-02/news/mn-959_1_eastern-zaire
The presidential guard was called in to lock down the capitol and quash the uprising, but between the soldiers mutinies and desertions and the bloodshed spilling over from neighboring Rwanda and Burundi, it was all over but the crying.
I don't quite knwo how to work in the Harry Potter aspect. According to Word of God it is about 1 galleon to 5 pounds. http://harrypotter.wikia.com/wiki/Galleon documents this. I believe serveral economists had a good laugh with that.
Then again, what I gathered from it was that it would be a very strong form of currency, being an inversion of this trope. Is there even an inversion?
Funny Money was renamed to Ridiculous Exchange Rates per TRS
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman