rather than trusting what Dell said, it would be quick to find out whether the psu is actually the culprit or not by using a  test psu.  I keep a handy working old 24/4 pin psu.
When I turned off the 7010 SFF I could not get it restarted. Orange LED was continuously blinking. I finally was able to get it going by pushing the back Power Supply Diagnostic button, and the Front Start Button at the same time. After about 24 hrs it stopped again. I did replace the battery, but still cannot get it to start by only using the front power button. The cpu fan seems to be a little loud. Could this cause this problem, or is it something else ? 
I have a Optiplex 7010 SFF that has a problem, and needs some help