I've used the sweetened condensed milk caramel many times. You can also cook it in a pressure cooker. Cook for 15-20 minutes with the regulator rocking slowly. Leave the cans in the pressure cooker until the cooker is cool.
Make sure to cool the cans completely before opening... I was in a hurry once and opened a can while it felt warm... boy, I had hot caramel all over my neck and face and all over the kitchen
Learned my lesson... I also make sure the cans are regular cans and not the pop up type.
Once the can is completely cool, I take the caramel out of the can and warm it on a sauce pan... stir with a whisk and can use this to cover your cake. 2 large cans will cover a 2 layer 8 inch round cake.