Yes, lower AWG number means thicker wire with greater current (amps) capacity, and your 16AWG 100' cord is too small for your new 10 amp trimmer. It is easy to find 100' 14AWG power cords, but they are a bit pricey like you said. Go to a local Home Depot store and look for their Husky house brand, which is less expensive than other name brands. You want a 14/3 indoor/outdoor medium duty cord.