As a cook, you have most likely had to deal with being out of an essential ingredient. If you are cooking Tex-Mex dishes like chili con carne, chili powder definitely falls into the essential category. That said, there is no need to panic if you are out of chili powder; substitutes are relatively easy to find. If you cook Latin American or Tex-Mex cuisine regularly, you may already have some of them in your kitchen.
Your best bet: Make your own chili powder from scratch
Chili powder is a mixture of spices and most of the components are readily available and widely used. This means that your best option for a substitute is to make your own. You can use 1/4 cup sweet paprika along with a tablespoon each of garlic powder, onion powder, and dried oregano; add 2 teaspoons of cumin to the mixture. Depending on your tolerance for heat, you can throw in some cayenne powder to taste.
Place all the ingredients in a tightly sealed container and shake it to combine them. Use it in the same way that you would use a premixed blend. Note that because manufacturers all use their own individual recipes for chili powder, you may not get the same results that you would with your favorite brand. Over time, you can play with the proportions of individual spices to get your desired flavor profile.
A decent second choice: Ancho powder
Ancho powder is used in many chili powder blends. It is responsible for most of the flavor that you get from chili powder. If that flavor is what you want, ancho powder should meet your needs. It brings a mild heat to dishes, along with smoky and fruity flavor notes. It consists of ground poblano peppers with no other additives. When using ancho powder in place of chili powder, add about half the amount that your recipe specifies for chili powder and work up from there.
In a pinch: Chipotle powder
Chipotle powder consists of ground chipotle peppers and has no other ingredients. Chipotle peppers are jalapeños that have been dried and smoked. Chipotle powder has a rich smokiness that will add a significant amount of flavor to your dish, even when used in small quantities.
Because chipotle powder is made with jalapeños, it does have the potential to make your dishes hotter than they would be with most premixed chili powder blends. Use it carefully. Start with half the amount specified in your recipe and increase in increments from there.
Harissa is a chili paste from North Africa that can be an effective chili powder substitute. It contains smoked chili peppers along with garlic and various spices like cumin and coriander. It can provide the chili flavor and subtle heat that you get from most chili powder blends.
If you prefer to stick with traditional Mexican ingredients, consider pasilla powder as an alternative to chili powder mixes. It is made from the pasilla chilies that you may have seen used in mole sauces and other popular Mexican dishes. Its earthy flavor pairs well with cumin and other spices used in Mexican cuisine; it works well in most dishes that require chili powder.