What this looks like is one half of a very old AT style power connector.
Early style PCs (286 up to somewhere around the early P2 era) used to have two of these white sockets right next to each other instead of the now standard ATX socket.
If this really is necessary for the motherboard to operate, then it's certainly not an industry standard for P3 Processors. I have built about 50 different P3 systems and Haven't come across a "half AT" power conector like this before.
Some motherboards manufactured during the transition from AT to ATX offered both connectors off the board so that system builders could use either style PSU, but I have never seen a board where both were connections were mandatory, especially not in a board as new as yours.
As the original AT connector had no feedback functionality (not even a soft power on, which was done with a big 230v mechanical switch!), so it may be that dell is just using this style connector as an easy way of connecting all the front panel buttons etc. Could you give us the motherbard model number, or post the relevant information from the manual if you have it? That would help a lot.