Ram upgrade for D07S (optiplex 9020)

DDR3 1600 RAM up to a maximum of 32GB total in 4 DIMM slots. Now will they work is the question. Dell systems are very picky about RAM makes and it is very possible that the Patriot RAM may not be compatible with the existing RAM. The ideal RAM to use is Crucial as listed here and to buy a kit of 4 if you want to fill all the slots. The other question, and Dell specs do not clearly indicate this, is whether 24GB of RAM is supported.

Hello sir and what about if I remove current memory, I can take a module out so we can check which one is it.

You can remove a memory module and attempt to match it which sometimes works. The trick is finding identical RAM. Just try to find a retailer that will allow returns if the RAM turns out not to be compatible. That is why I suggested Crucial as they will accept a return on RAM that is not compatible.

Re: It has 2x4GB 1600mhz DDR3 ram (4 slots), IDK if they must comply some standard or not.

fortunately the early Dell desktop models including 9020 and 780 are relatively easy going with aftermarket non oem desktop (non-ECC, unregistered unbuffered) ddr3 as long as the speed is ddr3-1333 to 1600 or pc3-10600U to pc3-12800U.  U means Unbuffered.  You can even mix same speed ram from different manufactures without issue. I have had both models and in my experience these models are not finicky as long as you use regular speed ddr3 that I mentioned for desktop only.  Do not use gaming ddr3 that has XMP or overclocked, and do not use speed higher than 1600.  I have seen 780 fail to post with higher speed ddr3.  Certainly do not use server grade ECC or registered, buffered ddr3 which are incompatible w desktop,

what JOcean was referring to are more recent Dell models using higher speed DDR4 memory such as Aurora R5+ etc.  those are a different story.  My take is as memory speed gets higher it is harder for Dell bios to deal with, thus it gained a reputation of being “picky“.

Speed (MHz) and volts need to match.  Otherwise, all RAM will be operated at the speed of the slowest stick.  If volts don't match, it won't work.

Like Crucial, A-Tech has a lifetime warranty and is a good way to save $ on somewhat older/older machines.  Not only have I used it for years, it works with another brand in my PC.  Not the only good name brand, just the brand I happen to use.

"Optiplex 9020 RAM" is a good search term for Google, Amazon, eBay, & etc.