The state of the Power Button LED on most Dell desktops indicates status.
My experience as a Dell field engineer shows that a blinking amber LED is not always indicative of a PSU failure. Beg, borrow or otherwise get hold of a PSU tester. Test the PSU as per instructions. If it shows the PSU is OK then it is another component. When Dell get a call about blinking amber LED then they send out PSU, Motherboard and front I/O panel. (Here in Europe anyway...they're covering all angles.
First thing I do on arriving at customer is test the PSU. If OK, the box stays sealed. Check all USB ports. If any are broken, then replace the relevant component (the front I/O panel or the motherboard). If the the front I/O panel looks OK then the mobo is replaced. This usually resolves the problem.
However, yesterday I came across a new one. The mobo had been replaced - no fix. I went along yesterday with an I/O panel, PSU and I/O panel to mobo cable.
Still blinking amber. Disconnected everything. Connected power cables one by one....all solid green until I connected the power cable to the Hard Drive. Blinking amber. The HDD was shorting. Back today to install a new HDD and reinstall OS/Drivers and Apps. All OK...very happy customer.