New Power Supply - iMac goes into Sleep mode

Just installed a new power supply in my mid 2011 Imac 27. Upon powering up, within a few minutes the imac goes into sleep mode, it seems. If I hit a key, the screen comes back up. When the screen goes black (what I believe is sleep mode as stated above), I can hear the fans also shutting down. After relooking at everything, a few times, I reinstaleld my old power supply. The Imac started up and runs fine…..no going into sleep mode.

A few points:

I wanted to replace the power supply because the Imac was completely shutting down at times, for no reason. It never went into sleep mode, it would shut off and come back up with a message about an unexpected shutdown.

With the new power supply, I noticed the fans ramping up in speed shortly after the imac powered on. This is unusually for this machine, the fans would only come on if the computer was in a heavy load condition and on for an extended time. With the old power supply reinstalled, the fans still have not come on (on for about 30 minutes so far).

Is this a bad power supply from Ifixit? The image from the website matched my power supply, I confirmed it looekd the same before I hit purchase. The one received does look different than mine….so it is different than the image on the website.