Instead of just cooling my one router, I thought I'd share the love with some other pieces of equipment too. I bought three older Noctua fans: https://www.noctua.at/en/products/nf-s12b-redux-700/specifications

I also bought a somewhat more powerful DC adapter (max capacity 27 Watts instead of 3.6), tied it all together, and now I'll shut up for good.

Thank you all! :)