Hi again, and you're most welcome!
Thanks so much for your very helpful reply.
Dry food is more fattening than canned, because it contains more carbohydrates.
If he vomits shortly after eating, and you still see pieces of food in his vomitus, this is more like regurgitation and can be caused by eating too quickly, swallow his food whole, as you mentioned, and the food being too close to or on the ground. To slow down his eating, place a new, washed golf ball in the middle of the bowl and this will make him eat 'around' it. Also, raise his bowls up to chest level, as this is better for digestion.
From your description of other symptoms, it's possible that Havoc may have developed diabetes. This will need to be tested for with a routine senior blood panel, including a thyroid test, from the vet.
For now, you're going to have to serve smaller, measured portions of food and perhaps consider changing to high quality wet food (considered healthier), which is high in protein and low in carbohydrates. Some well recommended ones are Wellness, Wellness CORE, EVO, Blue (grain-free). You can feed the wet or dry versions of these listed above, because they're grain-free and contain nothing artificial. I think you'll find this series of articles interesting, on the best way we can feed our cats, written by a feline veterinarian:
There is even a section on diabetes, should Havoc be diagnosed with it.
I hope you're able to arrange an appointment with his vet, asap, and all will be well with Havoc!
Please be so kind as to rate my answer with positive feedback, as that is the only way I receive recognition from the website for my assistance. Thank you very much!
Providing a positive rating will not end our conversation, should you need me for any follow-up. Simply click 'Reply to Expert' for clarification or additional information, if needed.