This model is inspired by the UNIVERSAL USB CABLE SAVER created by Engineering Projects. 

https://www.printables.com/model/1432772-universal-usb-cable-saver

I used the same method to provide strain relief between the neck of the DC jack and the cable.

I made this for two cables that were starting to show signs of wear. Both of the DC jacks are 5.5mm but the neck and cable diameter differ between the two.

The first one is for a cable diameter of 3.5mm, with a neck diameter of 7.5mm in the middle of the taper. The opening for the cable is 4mm with a 3.4mm entry slot and the opening for the neck of the jack is 7.8mm.

The second one is for a cable diameter of  6mm with a neck diameter of 10mm, The opening for the cable is 6.5mm with a 3.5mm entry slot and the opening for the neck is 10mm.

If you have another DC jack I can easily edit the model for a different cable and neck sizes, just let me know.

I printed this with PETG because I think PLA will be too brittle and risks breaking over time. I also printed it with 100% infill for added strength around the jack head. TPU might be optimal for this application.