This question can come up for a couple of reasons. First off, as pellet grills/smokers require a source of electricity, some think that the pellets are used purely to produce smoke, and they use electricity to generate their heat for cooking via an electrical resistance element.

Now, while this maybe the case with products such as the Ninja Woodfire, when it comes to conventional pellet grills/smokers, the source of heat and smoke are both from burning pellets. Therefore, in most instances, yes you have to use pellets in a pellet grill/smoker.

However, the question also comes up in terms of 'can you use charcoal or wood chips in a pellet grill/smoker?' In most cases, the answer is no, but you can actually get charcoal pellets now, so in that sense, yes, you can use charcoal in a pellet grill/smoker as long as you're talking about charcoal pellets.

With regards to wood chips, I'm aware that Lone Star Grillz promotes the use of wood chips in their pellet grills/smokers as a means to increase smoke production. However, in general, I would not encourage it, as many pellet grill augers will break trying to force wood chips through their auger tube.