My PC has a F_PANEL (2 x 10 pin Connector) on mobo of which 10,11,12,13,15,17,19 are pinless.
You don't have to use all of these pins if your case doesn't have the feature that the pin represents. Example your case may not have a reset switch therefore you don't need to use the RES- or RES+ pins. If you don't have fron speakers then you don't need to use the 4 Speaker pins and so on.
Have a look at your user manual to find out which pins are which and then cross reference against the names on your case wiring.
If your case wiring is a fixed plug then you may need to have the plug removed and the individual wires capped and tagged. It would be easier to buy a new case which would probably include a larger PSU then your DELL case anyway.
I am building a system using an ASUS A7V8X-X motherboard and an ancient Dell Dimension .... Case. There is a 20 pin System Control Panel Connector on the MB, but my case only has 15. I have been looking all over the internet trying to find a replacement system panel, but I can't find anything. I don't even know if I am calling it the correct thing. Just to clarify, this is the panel with the power and reset buttons, LED's, etc. I really don't want to spend the cash on a new case for something so minor, but...
I would appreciate any help.