The ESC works with all Intellivision models, including the original.
Some things to check:
Do you have a cartridge inserted into the ESC cart port when you turn it on? You'll get a blank screen without one. Note that the cart doesn't need to be an ESC-specific one. Any Intellivision cart will do.
If you have a cart inserted and you're still not getting a picture, you may want to clean the port connector on the ESC and the cartridge ports on both the ESC and Intellivision.
The Computer Adapter and Intellivison II use power supplies with uncommon voltage so you definitely need to use to the appropriate power adapter.
Hopefully, these tips get you up and running.