Most "400-in-1" requests involve the or similar "NES-on-a-chip" (NOAC) consoles. These devices come with the games pre-installed on internal memory, but a "ROM download" version is often sought for use on PCs or more advanced handhelds.
If you are looking for a digital version of this specific compilation, several archive and community sites host the files: 400in1 nes rom download new
Which of those would you like?
: Provides clean, high-quality versions of original NES games if you prefer to build your own 400-game collection. Essential Emulators 400in1 nes rom download new