What is the button on power supply of the Dell Optiplex 760 workstation for?

What is the button on power supply of the Dell Optiplex 760 workstation for? There is a small button near LED power indicatior - seems to do nothing when pressed.

Solution 1:

It has a green LED above it and is used to test the PSU without opening the case and testing the PSU.

I have one here in my office and I believe thats what it does.

Note that when plugged in and pressed, it fires up the PSU for just a second.

Solution 2:

It's called the Built-In Self-Test (BIST) for the power supply. The BIST can be used to isolate and troubleshoot power failures throughout the system.

Here is a video from Dell about it: https://www.youtube.com/watch?v=udGOe7LQJEI