How do I get my Dell 4K monitor to power my mac mini M2 ?

The Mac Mini must be plugged into a wall outlet using the supplied power cord.

Then you connect a display to the Mac mini, as per > Connect a display to Mac mini - Apple Support

I am not familiar with a M2 but every other Mac computer I have ever seen requires its own power source. I would think that unless the monitor has a standard socket where you can plug in the Mac the way you would into a wall socket that this isn't possible unless the M2 is radially different.

Again I am not familiar with all the notebook models. If you say it worked then it is conceivable that as a mobile notebook model which is battery charged, that it could take charge from a USB/Thunderbolt port.

The mini is a different computer. It is not battery powered. It is designed to be powered from mains circuitry.

MacBook Pros have internal batteries. They are designed to accept power via USB-C Power Delivery (or other means, such as MagSafe 3). Logically, they must have some way of obtaining enough power to start USB-C Power Delivery negotiations in the first place – and a way of charging batteries that are nearly or totally drained. That's because "running out of battery charge" is an everyday occurrence for laptop computers, and their design anticipates that.

The Mac Mini designers would have known, as a baseline, that the Mini would always have access to wall power. So there would not have been a need to design the machine to be powered over USB-C. Just because USB-C is able to support a wide range of capabiities does not mean that every USB-C device has all possible capabilities.

You can not power the Mac mini via a Thunderbolt/USB-C cable.

The Mac mini must be plugged into an outlet using the supplied power cord.

Not possible unfortunately.

You're welcome.