interpreting stickers on RAM

Does anyone know how to read the labels on RAM? Or have a link to a good resource for reading the labels?

Here's why I'm asking:

I have a third-party Dell server in my rack. The vendor sent us additional memory to install, but it doesn't work. The single stick already installed says PC3-10600E and the one they sent me says PC3-10600U. The *U one does not work, even by itself. I'm trying to figure out the difference between *E and *U.

It's the difference between ECC, Registered and Unbuffered RAM. (E, R, U)

You want more of the "E" RAM if that's what was there in the first place. Typically, they do not mix. The server should have RAM and DIMM population guidelines listed on the chassis cover.

Also see: HP DL160 G6 memory PC3-10600R vs PC3-10600E