How can I adjust the powder filter to show all powders?

In the calculator, you have to select the caliber first. The system checks if it is a rifle or revolver/pistol caliber. 

By default, it then only shows suitable powders in the powder dropdown, i.e., for rifle calibers, the system only shows rifle powders, and vice versa. 

You can change this default setting in Settings under Calculator Preferences to always show all powders.