What's the LED, 12V? Any PWM 12V dimmer should work. Cheap as chips on Amazon.

I'm working a new build idea (not posted yet) and wanted red-only LEDs under the PSU shroud 'glowing' thru the openings a bit, had some 5050 RGB strips from long ago not used anymore. +12V to the common port, return to the "R" out of the RGB 3 remaining pin options, on the output of this, input side plain old 12V from a SATA or any other connector. Knob controls brightness.

(I intend to just set-and-forget inside my case).

The linked one is about $10 but that's for 4...not sure if you can easily find singles but I'd bet ebay would also work: https://www.amazon.com/gp/product/B07L74P6B3/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&psc=1