I you get a 25 ft, 14 guage, you'll be fine. Imprinted on the wire insulation will be codes including "14AWG" and that's what you want. It'll also cost more than the more common 16 guage cords. Of course you want a grounded cord, that is the ones with 3 prongs and 3 holes.
If you're really frugal, you could maybe convert the new 25-ft to a 10 and a 15, or something like that, if you only need a shorter length for your smoker. Buy one plug and one receptacle and make two out of one. But if you've never done any wiring, probably best to just us the new whole cord.