TL;DR: avoid Digitus AC fans, but use DC case fans with built-in/external temperature controller plus 12V or USB-step-up power supply and optionally fan grilles/meshes.
A while ago, I bought a 7U shallow 19-inch rack cabinet to house some of our network equipment for the offices and other rooms at the top floor: [Wayback/Archive] DIGITUS Professional Network Wall Housing – Soho Wall Cabinet: Amazon.de: Computer & Accessories
Since it was to be mounted in the boiler room, which is on the top floor under a flat roof, it would get warm so I wanted fans installed in it under or over the air vents in the housing (the cabinet is delivered as flat-pack with parts pictured below and requires about half an hour assembly time):
The Wiert Corner - irregular stream of stuff 