I don't think you did check. Over the past 10 years this question has been answered and answered and answered. QX9650 (130W) is a no not EVER.

https://www.dell.com/community/Desktops-General-Read-Only/Optiplex-755-Processor-Upgrade/td-p/3845249

Bios needs update BEFORE changing CPU.

Will be bricked if antivirus software is installed or you try using windows 10 to update.

XP or MSDOS to update bios.

https://www.dell.com/downloads/global/products/optix/en/opti_755_techspecs.pdf

Officially validated for all EXCEPT USFF

Intel Core 2 Quad Q6700 Processor (2.66GHz, 8MB L2 cache, 1066MHz FSB, VT)
Intel Core 2 Quad Q6600 Processor (2.4GHz, 8MB L2 cache, 1066MHz FSB, VT)

The Q9650 worked in my minI tower bios A20.

 Later Revisions with the Copper Performance heatsink with heat pipes.

 Quads
N652J 3.00GHz Yorkfield Quad Core Q9650, 12MB 95W
F886J 2.83GHz Yorkfield Quad Core Q9550 12MB, 1333FSB, E0 
N650J 2.66GHz Yorkfield Quad Core Q9400, 6MB, 1333FSB, R0
MP627 2.66GHz Kentsfield Quad Core Q6700, 8MB, 1066FSB, G0

I didn't mention QX9650, just the Q9650.  That processor was out before A10 BIOS.  Yet BIOS would still need upgrading?

I mentioned I have the pdf manual already.

I checked and it shouldn't be hard to take my word for it.  I saw that same posting, but only saw the Q6600 some for reason, probably tired.

There's also a glitch with images.  If I'm signed in, most images don't show.  If I sign out, the site backs up to initial Dell Community screen.  So if I go back where I was, I have to have ways of remembering, like if it's a newer posting I can find right away or bookmark it.  I can't always tell when I'm not seeing images while signed in, especially if some show and some not.  I know about the image indicator.

I want to be secure after hours of reading, because although the SFF shares all yours features with DT, aren't the same (I believe), and I haven't read in any way about customization for this model (DT). So... :

The best configuration without any dangerous hack for the Dell Optiplex 775 (DT, not SFF) can be the next? (The steps are ):

1. Upgrade the BIOS to the last version. (A22 actually) (done)

2. Upgrade the power supply to +500W. (waiting...)

3. Upgrade to 2 GB RAM high-density DDR2 800MHz x 4. (8 GB) (working...)

4. Upgrade the processor to Intel® Core™2 Quad Processor Q9650. (12M Cache, 3.00 GHz, 1333 MHz FSB) (stoped...) (Need feedback)

5. Upgrade the Graphics Card to 1050 Ti. (Possible?) (stoped...) (Another more lower working...) (Need feedback)

6. Upgrade the HDD to 500 GB. (maximum, no?) (done)

7. Upgrade the Operative System. (done) (relatively)

Firefox Friend, please, don't kill me. U_U

good day! I have a DELL optiplex 755 SFF PC. It has a 275W power supply, 8GB of RAM at 800mhz, BIOS updated to A22, 500GB of SATA Hard Drive and has a Core 2 Quad Q8400 processor at 2.66Ghz, 95w and 1333mhz bus speed. I want to upgrade my processor to the Core 2 Quad Q9650. My question is ... if I can upgrade my processor to Intel Core 2 Quad Q9650? I would appreciate your answer.

Hi @Alejandro123xdxd,

You can absolutely put a Q9650 in it.  I ran my previous 755 (with Q9650) with OS on an SSD and HDD for storage.  Did that PC ever fly.

Storage HDD shouldn't be mistaken for backup.  Backup should always be outside the PC in case of malware or virus taking out both drives.

A Dell Optiplex 755 MT Can be upgraded to Q9650 and 8GB DDR2 RAM. Even you can upgrade the graphics card to Radeon HD 7570. 

to everyone in this thread, and specifically bradthetechnut (encouragement) and speedstep (need to speak softly in case you have to eat your words), I have a bunch of Opti 755 USFF with not only a QX9650 and 16GB of ram, but the original PSU as well, and they have been running that way for years. I actually have them running Windows Server 2016, too.

Give me a way to post the pictures of the BIOS screens, in case you want proof.

Dell often publishes a ram spec of half the actual supported amount.