There are only five known variants of AC plugs for boomboxes.
1) Full rectangular with squared-off corners
2) One end with rounded corners - other end with squared-off corners
3) All corners rounded - looks like an oval
4) All corners rounded with notches in the middle - looks like the number '8'
5) One end with rounded corners - other with squared-off corners with notches in the middle
You will need to check the female plug on the boombox to know which one you need. However, the #4 plug above should fit almost every boombox.