FWIW,  Dell cases and front panel connections are proprietary and undocumented on most.  Same way with fan motherboard connections.   

Some newer models use an 8 pin power connection and not the standard 24 pin.

For the 8 pin, I'll just get an adapter

Re: Will this void the warranty for the whole pc

Dell will not support you moving parts to a new case and any issue in the non-Dell case.  If you want to keep warranty when issue arises, you would need to move all components back into Dell case and make sure nothing is lost or damaged due to technique.  Dell does not mind you taking out and putting back OEM parts, as long as the system is still running in 100% Dell environment.  bear in mind of course if you break some part due to improper technique, such as bent socket pin, that would be considered outside warranty.  Warranty covers manufacturer defect but no user incurred damage.

New case would void the warranty.

So you would have to put it back to the original case if you wanted service.

Dell does not document pinouts so you would have to know what you are doing to prevent startup errors.

Yeah, but what I'm afraid of is dell making up connectors on the mobo. Do I have to worry?