What is Underinsured Motorist Conversion coverage?

I am confused how this is different from Underinsured Motorist coverage and which of the two is best?

Underinsured Motorist coverage pays for injuries that you and your passengers may suffer in a crash where the other driver is at-fault and the other driver does not have enough liability coverage to pay for all the injuries caused in your vehicle. It's easiest to explain this as an example: You are hit by another driver that carries the state minimum liability limit (which is $20,000 per person) and your injuries total $30,000, meaning your injuries exceed the coverage limit of the other driver's liability. If you carried an Underinsured Motorist limit of $40,000 per person, then your policy would cover the additional amount of injury up the $40K limit you selected. Underinsured Motorist Conversion coverage does essentially the same thing except the amount you carry pays out in ADDITION to the other driver's liability limit, so in this scenario, you could claim up to $70K worth of injuries for any one individual in your vehicle. **Conversion coverage is an option that is specific to the state of Connecticut and not currently available in any other state**