Some TV's it will work and other it will not.
I just recently got a generic MHL cable for my Galaxy SII and plugged it into my Sony Plasma screen TV (more than a few years old at this point)--nothing, I get a quick flash and it says 480p in the upper corner but I can get no picture and I tried all of the usual solutions, restarting, plugging them in in a different order--nothing.
I was about to return the cable thinking it was junk, but I decided to try it on another TV.
I plugged it into my LG plasma screen (less than 2 years old) and immediately got an image.
It would appear that certain older TVs just don't work with the adapter.
Before returning them, try it on a different TV...remember this is a relatively new 'standard' and they (Samsung) may not have all the kink worked out yet.