Question : Problem: Dell 4600c Blinking Amber light on MB and power button

i am working on a Dell Dimension 4600c.

This machine will not power up, it has a blinking amber light on the MB, and the power buttton on the front steadily blinks amber.

I assumed it was the power supply, so I took one off the shelf and tested.  it worked.  So I ordered new PS.  Got it in, and that one didn't work.

Digging deeper, I tested the original PS with a PS tester, and all checks out.  Tested the GOOD PS off the shelf, and it tested good as well.   Tested the new one, and it is flat bad

Why will 1 PS work,  and the other won"t

What am I missing here?

Answer : Problem: Dell 4600c Blinking Amber light on MB and power button

a tester does not test all functions and loads of a PS; just with a given load.
it can also be your original PS is an aged one; PS's loose power with age (you can even put it in the PS calculator :  http://extreme.outervision.com/psucalculatorlite.jsp    )
so a power supply can test ok, but will not work with full load