HP AD276A 8GB (2 x 4GB) DDR2 SDRAM.

These are PC2-5300 memory modules, which were returned by a customer who did not use them because she quite incorrectly thought they were the "wrong" part and that "they have completely wrong specifications". Actually, PC2-5300 is backward compatible with PC2-4200:

http://haneefputtur.com/difference-between-pc2-4200-ddr2-533-pc2-5300-ddr2-667-pc2-6400-ddr2-800-and-pc2-8500-ddr2-1066.html

That's why vendors sell both of them as AD276A:

https://store.flagshiptech.com/hp-integrity-rx2660-memory-kit-ad276a-8gb-2x-4gb-ddr2-pc2-4200-pc2-5300/ 

They serve the exact same purpose. Please, get better informed and actually know what you are doing before buying something, otherwise it only ends up wasting the seller's time and money with unnecessary returns.