Instead, Dell uses a (2x5) but with a proprietary keying and voltage layout. In many OptiPlex models, Dell integrates the power button, hard drive activity LED, and speaker into a single plastic housing. Worse, Dell often moves the Power LED to a completely separate 2-pin header elsewhere on the board.
Dell MIH61R motherboard (commonly found in the Dell OptiPlex 390 dell mih61r mb front panel pinout
For a cleaner and safer installation, many users recommend a Dell Front Panel Header Adapter Instead, Dell uses a (2x5) but with a