I did this recently with pesos, for a trip to Mexico. The exchange rate and the fees weren't the best, and it took 2 days to get the money. However the USD to peso conversation was so favorable, that I still came out ahead over using US dollars on my trip. I would consider doing it again, just to get enough currency to start my trip. In Mexico, many cambios were shut down due to money laundering concerns. They are much easier to find in Jamaica.