This is a case for the cheap Banggood mp3 decoder

https://www.banggood.com/Bluetooth-Car-LED-12V-MP3-Audio-Decoder-Board-Remote-Control-FM-Radio-USB-SD-p-1135090.html

On the backside are holes for a 12 V powerconnector

https://www.banggood.com/1Pc-DC-Power-Jack-Socket-Power-Outlet-Power-Socket-Female-Panel-Mount-Connector-p-1177643.html

and a cinch feedthrough

https://www.banggood.com/Audio-Binding-Post-GoldPlated-RCA-Chassis-Panel-Sockets-Connectors-p-929292.html

I use this device to play mp3 from an USB-Stick to my amplifier. I am very happy with the sound quality (sounds just like from spotify), but without any PC fan noise. There is a shuffle mode and a remote control (cheap china style) with the device.