Power blackout and fan protection options:
I recommend a UPS because they're readily available, and will emit annoying beeps in a blackout, while still suplying power to your critically important ventillation fans. You could also use one of the following solutions, that require less money and more DIY engineering. Do not try these at home unless you are comfortable with electronics soldering and prototyping, as your life may depend upon your ability:
- Use an electromagnet that plugs into a wall outlet, as the latching mechanism for the enclosure's doors. Then when the power goes out, the electromagnet releases, and the door can be rigged to fall open when not retained by the magnetic field.
- Use a blackout buzzer, powered by a battery, that will keep buzzing/screeching to wake you up when the wall outlet, and your fans, lose power.
- Use a fan failure alarm (Amazon) to wake you up when one of your 12v 3-pin (with yellow RPM wire) fans stops spinning.

Any reason you aren't using something made for fans?

https://www.amazon.com/Temperature-Control-Speed-Controller-Module/dp/B019P0FLHW