Can I substitute nespresso espresso powder for instant coffee in a devil's food cupcake recipe?

Nespresso capsules are filled with ground espresso, it is not instant. I would not recommend the substitution.

And sometimes an article here can address the very issue you asked about.
See this on adding coffee when baking chocolate cakes
https://food52.com/blog/19688-this-ingredient-will-make-your-chocolate-cake-taste-more-chocolatey

Yes. As long as it's instant espresso powder.