Does it have a door flap to cover the front? It should also say "Duo Dock II". The lids are interchangeable. So it's possible someone swapped them for some reason. It should look like this: http://img.wiki.excite.co.jp/upload/apple/33/33181428ef35c158f090dcf4b6e18f35_600x354.jpg
The original dock looked like this and just said "Duo Dock": http://img.wiki.excite.co.jp/upload/apple/2f/2fb9b9a6b58d8dc421703053cb5d499a_600x418.jpg
The first Dock had the Snow White stripes on top. The Dock II was just a smooth flat top, no lines as was the Plus. There may have been a revised original dock which added the door flap and/or removed the stripes before the Dock II lid was released, but probably not. http://developer.apple.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-68K_Portable/PowerBook_Duo_Dock_II.pdf
Apple indicates the stock Duo Dock II should support a 280c. If your lid has lines on top and no door flap, then it has definitely been swapped somewhere along the way. If not, it may still be an original lid, or you may have a problem inside. It's easy to remove so you can check. http://docs.info.apple.com/article.html?artnum=13740-ja
Interestingly the Duo Dock Plus looks just like the Dock II lid except it says only "Duo Dock", like the original: http://img.wiki.excite.co.jp/upload/apple/41/412f9c2d434f5dd58cbff94f11909172_600x363.jpg
FYI, the dock works just fine without a lid, though that doesn't do you much good if you want to set a monitor on top. Then again, it might be fun to put a sheet of glass across the top so you can see the inner workings.
EDIT: Here's some good ideas, including cutting off the front half of the useless lid: http://www.mail-archive.com/duolist@themacintoshguy.com/msg02897.html
The original dock looked like this and just said "Duo Dock": http://img.wiki.excite.co.jp/upload/apple/2f/2fb9b9a6b58d8dc421703053cb5d499a_600x418.jpg
The first Dock had the Snow White stripes on top. The Dock II was just a smooth flat top, no lines as was the Plus. There may have been a revised original dock which added the door flap and/or removed the stripes before the Dock II lid was released, but probably not. http://developer.apple.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-68K_Portable/PowerBook_Duo_Dock_II.pdf
Apple indicates the stock Duo Dock II should support a 280c. If your lid has lines on top and no door flap, then it has definitely been swapped somewhere along the way. If not, it may still be an original lid, or you may have a problem inside. It's easy to remove so you can check. http://docs.info.apple.com/article.html?artnum=13740-ja
Interestingly the Duo Dock Plus looks just like the Dock II lid except it says only "Duo Dock", like the original: http://img.wiki.excite.co.jp/upload/apple/41/412f9c2d434f5dd58cbff94f11909172_600x363.jpg
FYI, the dock works just fine without a lid, though that doesn't do you much good if you want to set a monitor on top. Then again, it might be fun to put a sheet of glass across the top so you can see the inner workings.
EDIT: Here's some good ideas, including cutting off the front half of the useless lid: http://www.mail-archive.com/duolist@themacintoshguy.com/msg02897.html