display thunderbolt alimentation cable problem

Hello

I recently met a strange problem with my Thunderbolt screen. I use a Retina MacBook Pro with the supplied adapter to the power cable.

Here's the problem: When I plug in my computer, the power supply doesn't connect itself as before. The LED does not light. I have to plug and unplug several times connector to eventually turn on. However, if I plug the cable (without adapter) on an old MacBook everything works normally.

The adapter is a vey little and passive part and I can't believe it's broken.

Thank you for your help.