There is absolutely nothing "diabetic" about the food the vet just tried to sell you and in many cases the ingredients are not as good as Fancy Feast/Friskies or any other LC wet food. If the vet had you buy some, just remove one can from the case and return it to the vet because they have a money back guarantee from the manufacturer and tell the vet Ted won't eat it.
Fancy Feast Classic (Pates) or Friskies pates are perfectly good, actually better and inexpensive alternatives.
One word of caution......if Ted has been on a high carb diet you will have to be careful putting him on a LC diet with insulin in the picture. Did the vet discuss home testing with you? If not, please head over to the Health Forum and post there for some diet and testing information. We can explain more there and get you on the right path to keep Ted happy, healthy and safe.