If you want to bump up the ABV in a cider I'd recommend using some good apple juice concentrate, along with the extra sugar. Make sure that the concentrate doesn't have anything added to it that might inhibit yeast, like sorbate.
Pay attention to what alcohol tolerance the yeast has. I've heard of people using dry yeast packets intended for wine (*should* easily go up to 11% abv) or Nottingham ale yeast (you *might* have trouble getting past 9% abv if you don't oxygenate), but there are yeasts out there intended specifically for cider.