More often than not a customer will go to replace their Roady or Roady 2 Power Adapter and find that the new one does not fit. This is an easily fixed problem and is caused by the o-ring from your previous power adapter breaking off and getting stuck in your Roady or Roady 2. To resolve this issue all you need to do is take a pair of needle-nose pliers and remove the stuck o-ring from inside of your receiver. Now your new power adapter should fit perfectly!
If you are unable to remove the stuck plastic piece using a paperclip you can use a T5 driver and disassemble the receiver. Once taken apart you can break off the black plastic cap and remove the stuck plastic piece that way. This, however, should be a last resort and is NOT recommended.
I had this problem earlier and got it out. Just had my second AC power supply go bad. It is outputting 9 volts instead of 6 volts. Existing 12 volt supply for car working fine. Ordered new 12 volt supply for use with 110 volt AC/12 volt DC home supply. Plug different size. Will not work. Very annoying.