Adapter not working

Laptop XPS 13 9380 is 2 years old and out of warranty.

Suddenly the battery is not charging, and % is running very low. The red flag went up when:

- the display is not as bright as usual.

- when not in use, it does not just sleep, it turns off and the power button has to be pressed to bring it back to life.

All cords and plugs are firmly attached. No damage anywhere. The laptop has not been moved in over a month. The wall receptacle is working fine.

I ran the diagnostics test and all it told me was that the adapter was not working. Duh!

What to do? Do I need a new adapter? Doesn't seem right, after only 2 years of use.

I read somewhere that I can use any USB-C cord and outlet plug (such as from my iphone or ipad) to plug into the adapter spot to charge the laptop battery.  Seems too easy.

Please advise--thanks.