I get an error about a missing DLL on startup. How do I fix that?

Snes9x on Windows requires DirectX 9 to use the Direct3D and XAudio2 outputs. You can install it manually from here (you only need one):

Websetup, will only download necessary components

Redist, contains everything

If you have trouble with the above, here is an archive link for the old redist installer: https://web.archive.org/web/20201216110836if_/https://download.microsoft.com/download/8/4/A/84A35BF1-DAFE-4AE8-82AF-AD2AE20B6B14/directx_Jun2010_redist.exe

Will that replace the existing DirectX 10, 11, or 12 installation?

No. It will only install an extra part of DirectX no longer automatically installed with Windows.

Most games install these parts secretly during their own installation. We don’t use an installer in order to make it easier to move the Snes9x install around. Also, some download sites have been known to repackage install programs to include spyware. Making Snes9x “unzip and you’re done” prevents them from doing that.

That still doesn’t fix it.

If you still experience problems use this link instead:

https://www.microsoft.com/en-us/download/details.aspx?id=6812

It’s a large download, so definitely try the other installer first.