For sharing only. Happened to me on my Roland MC-909.
At your own risk, find another same plug head as the one that got its tip stuck inside the machine. Use superglue on this plug (think about the area that would adhere then apply only to that portion.
Stick it in, wait for it to cure and pull.
I was so relieved to get mine out. The box still worked as before and lesson learned - would never use/buy a cheap plug on a machine I value again! 
Good luck!