Can my Dell Optiplex run 16GB of RAM?

Probably. Dell’s official specs are conservative, but the chipset usually supports 16GB even when Dell only certifies 8GB. You need the right stick type: 2Rx8 or 1Rx8, 1.5V, non-ECC, unbuffered. Avoid 2Rx4 or high-density sticks. Older models (790, 7010) often max at 8GB per slot, but newer ones (3020, 7040) usually take 16GB fine. Check user forums for your exact model before buying.