I was testing to see if my fan would run, so I Ran Furmark for 5 minutes. My GPU got to 93 degrees, yet the PSU fan never turned on. It works when ECO mode is off, but it's really noisy. Is my PSU broken?

Hi yallah,
 
ECO mode will not turn the fan on until it is needed.  Please understand that just because the graphics card is taking load it does not necessarily mean that the PSU will need to turn the fan on.
 
It does not sound like anything is broken for you.
 

yallah
I was testing to see if my fan would run, so I Ran Furmark for 5 minutes. My GPU got to 93 degrees, yet the PSU fan never turned on. It works when ECO mode is off, but it's really noisy. Is my PSU broken?

if your rig runs fine, no crashes or BSOD your PSU is most likely running fine as well.
if the PSU fan doesn't spin then your PSU just doesn't need cooling, that's a good sign.
during the last 6 months I never saw my PSU fan spinning, even during the hottest summer days.

I would like to piggy-back on this thread if possible.  I am having an issue with my 850 G2, where my graphics card (MSI GTX970) will quit working or the NVIDIA graphics driver will crash, only when ECO mode is switched ON.  When I switch ECO to OFF, the issue goes away (tested over spans of 1+ weeks).  This occurs during either web-browsing or during a gaming session.  I have benchmarked the graphics card and updated to the latest drivers to ensure the issue is not with the card itself.  
 
Preliminary Google searches yielded insight that this issue could come from power-supply issues, mostly from it not supplying enough power to the GPU, which is why I tried switching ECO mode OFF to test this.  I'm just curious if anyone else has heard of this before, or if there's something else I might be missing?  The fan noise with ECO OFF is now the most audible component in my build.  Thanks!