780 DT, Core 2 Quad Q8200S

Should work as the Core 2 Quad was a supported CPU in that model. The socket, TDP, and BUS speed is the same. And according to game debate the quad is about 24% better performance than the core 2. The tricky part could be finding the CPU as the Q8200S is about 9 years past the release date. Probably the best bet is Ebay.

I found a Q8200S on Ebay for 15 bucks plus shipping, and was thinking of getting it. Do you think I will be able to get a regular wattage model like the Q8400? Or is that too much for the 255w PSU to chew?

In case you didn't find an answer yet...  The 95 watt Q8400 shouldn't be any trouble for your PSU.  You could go up to a Q9650, which is also 95w.  I've found it on eBay and Amazon.

Thanks for your reply. I do have one more question, would I be able to add a Radeon HD 7570 or similar graphics card to this, on top of something like a Q9650? I'm thinking of turning this into a low to mid-spec budget Gaming PC.

Top answer on Google with its source included:

"The Radeon HD 7570 requires 60 Watts to run but there is no entry for the Radeon HD 7750 Sapphire 2GB DDR3 Edition. We would recommend a PSU with at least 400 Watts for the Radeon HD 7570 and a PSU with at least 400 Watts for the HD 7750. The two GPUs have been recommended a PSU with the same amount of wattage.

AMD Radeon HD 7570 compare AMD Radeon HD ... - Game Debate

https://www.game-debate.com/gpu/index.php?gid...radeon-r7...radeon-hd-7570"

Yet, on eBay:  Dell 780 DT with Radeon 7570 - eBay

With conflicting resources, I can't be the one to decide on whether to try it or not.  One idea if you want - Contact the seller of that 780 DT to see if they did anything with the PSU.

When I Googled "radeon hd 7570 wattage," it didn't even look like my 305w PSU would be enough.

The one that seemed to short on you, the GT 1030, was suggested in Dell Community:  GPU that will work with my dell optiplex 780 DT

From Tom's Hardware:  "I got a spare Radeon 7570 from Dell XPS 8500 and put it into a new Gateway SX2110G (slim desktop) with only 220W PSU. The graphics worked well. I use Win 8.1 so the computer automatically find the driver for the graphic card. By the way, the Dell XPS is a normal size desktop."

I also Googled if the 780 DT can run a Radeon HD 7570.  I leave the informed decision up to you.  With your 255 watt PSU, minus the processor and GPU, you'd still have 100 watts left over.

I also check Dell Community as a source, sometimes just going in from Google.  I noticed you started another thread with the same question.  It looks like you might as well try it; it looks like it could work.

Thank you for your informative reply. I looked at the seller's description, without any luck in seeing if they did anything to the PSU. As you recommended, I will probably ask them if they did do anything to it. Again, thank you for helping me solve the many issues I've had on the Dell Community. I might end out trying this mix of parts, and probably have a backup motherboard or PSU ready to go if things go wrong.

You're welcome.  And thanks for clicking "Accept as solution" where you deem fit and the kudos.  It's nice knowing when one is satisfied with an answer.

A little fyi in case the question comes up:  The PSU in a 780 DT isn't upgradeable.  In an SFF, one can go from 235w to 280w out of an Optiplex XE PSU, but that would only give you 25 more watts even if it were possible.

Good plan you have with having backups handy.

Let me just confirm: This works.

I put in a Core 2 Quad Q9400 and Radeon HD 7570. I had a bit of ram issues with the Core 2 Quad (I had to reseat the ram so both sticks were in the same colored slots), but other than that, it worked. The 7570 booted first try, and I even ran a stress test with an overclock and it held up great.