Powering arduino 5v dc

I'm trying to power my arduino using a 5v 3A dc adapter which i plug into a female dc connector and then to a USB cable. The arduino wont turn on and I can't figure out why this wouldn't work

Any ideas?

What is the voltage measurement across the exposed wires?

Try plugging the wires into the 5V and GND pin and see if it turns on like that

You can just connect the external 5v power supply to the Arduino 5v pin and GND PIN.

I've actually already tried to connect it directly to the 5v pin and GND and still no luck. That's why I attempted using a cut USB cable

What voltage have you measured on the bare wires when the power supply is disconnected and connected to the Uno?

When not connected to the UNO it just keeps ticking down into the negative. When connected to the UNO it seems to jump up and down a lot. Not sure what to make of this. Not sure if I trust my multimeter.
The power adapter is brand new

So if the power readings are bad, would one expect the Uno to run well or at all?

Are you sure you're measuring correctly? If yes, it sounds like a bad power supply to me.

I'm not 100% sure since this is the first time I use a multimeter, but I think I'm doing it correctly. I'll try another power supply

You can get more advice by posting a photo of the your setup that power supply voltage is measuring by DMM.

This is my multimeter on the setting im using. then i put the black probe on negativt and red on positive


I've tried to use a 12v power supply. Connecting it straight to the barrel jack works but when I'm hooking it up like this, it still wont boot.

I'm getting weird readings using this power supply as well. it seems to hoover around -2.3

You can post a new photo that measures the voltage by connecting only the DMM probe to the adapter that converts the barrel jack to a wire connector on the upper side of the second photo?

Update. finally got it to work! seems the female dc connector waa the culprit. I tried with another one and now it works

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