After a days of googling I decide to try to get answers from Dell experts.
So, I need some help to choose DACs to connect different devices (Next there are just cases):
1) Connect a Dell Poweredge R820 with a QLogic 57840S adapter (Quad port SFP+) to a Cisco 3560X
2) Connect a Dell Poweredge T430 with an Intel X520-DA2 adapter to a Cisco 3560X
3) Connect the R820 to the T430
I want to ask also witch SFP 10G SR MM transceiver should I chose to connect Dell servers to an optical fiber (Cisco ones can work without issues, or should I take Dell ones, or a transceiver for each brand)?