I've managed to have success getting adapters plugged in to the Colecovision for the purpose of getting Playstation controller compatibilty.
Watch the experiment in action here:
Here are the adapters you'll need:
1) 9 pin Sega Genesis extension cords (2)
2) Edladdin Seagull 78 controller adapter (converts Genesis controllers to be fully-compatible with the Atari 7800)
3) Tototek Joypad Converter version MD (converts Playstation controllers to be compatible with the Sega Genesis console)
4) PS1 Multitap
5) Speedlink Redeemer Beyond Total Control Playstation 2 mouse/keyboard adapter
6) powered USB hub with power supply
1) Plug in a Colecovision controller into port 2 of your Colecovision (consider connecting a 9 pin extension cable to it in case you want to sit a little ways away from the console.)
2) Plug a 9 pin extension cable into port 1 of your Colecovision, but don't plug any adapter into it yet. (wait)
3) Connect all the above adapters/PS1 Multitap together but leave the Seagull78 adapter unconnected to the 9 pin extension cable that's plugged into port one of the console.
4) Plug your Playstation controller into port A of the multitap
5) Plug the Speedlink Redeemer into port B of the multitap
6) Connect a powered USB hub (with power supply plugged into the wall) to the lower USB connector of the Speedlink.
7) Turn on your Colecovision and use the keypad of the port 2 Colecovision controller to make your game selection and start up the game.
8 ) Now plug in the adapters to the extension cable that's plugged into port 1 of your Colecovision and play your game with the connected Playstation controller.
This method works for many, but not all Colecovision games. The ones that are incompatible with this method are the ones which don't allow a keypad controller that's plugged into port 2 of the console to start up the game, but only a keypad that's plugged into port 1 of the console. If you want to know how to get around that with a 9 pin splitter cable method, take a look at the video presentation.
The nice thing about using Playstation controllers is that both buttons- not just one button- will work in the games that have the 2 button access.
Another really nice aspect is that you can use a flightstick to play games like Zaxxon and River Raid. Also, it's nice to be able to use an arcade stick to play games like Q-bert or Ladybug.
There is a new development on this. In the U.S., the Speedlink Redeemer adapter (which is a mouse/keyboard Playstation controller adapter) that I've used is hard to find. Well, I've got a new solution to solve that. Replace the Speedlink with a Brook "Game Controller Super Converter" (a PS3/4 controller to PS2 console adapter). This is a much easier adapter to find. I'll show you what both adapters look like: http://i.imgur.com/Mrf3qmA.jpg