HOWTO – Switching on/off a DC motor with a Raspberry Pi – www.DavidHunt.ie
pi 2 - How to control the 5v output from raspberry pi to open and close a relay - Raspberry Pi Stack Exchange
Amazon.com: [20W 5V 4.0A] Raspberry Pi 4 Power Supply, iUniker 20W USB C Power Supply with ON/Off Switch 5 V 4 A Raspberry Pi Power Supply for Raspberry Pi 4 Model B
turn off fan by shutdown only - Raspberry Pi Forums