There's always Dell Spare Parts (1-800-372-3355) for the PSU, but you'll probably pay more... And lots of threads about PSU and GPU upgrades for the Inspiron 3670.
I own an Inspiron 3670 desktop that has an Intel i5-8400 CPU, 12 GB Ram, 128 SSD, 1000 GB HDD, and Win 10 OS. It also has the 290W power supply and the Intel UHD 630 on-board graphics. I am planning to upgrade the power supply as well as the graphics. I have two questions regarding this upgrade: I would appreciate any input, thoughts, and opinions to my questions regarding acceptability and functionality.
Inspiron 3670 – Power Supply Unit & Video Card.