I have a combination of X7SPE-HF-D525 mobo and CSE-503L-200B chassis and I confused a little bit because the mobo has 24pin power connector but at the chassis has only 20pin?
Because this is an Atom solution, you do not need a 24 pin power connector. Just use the 20 pin in the 24pin connector on the mainboard. It will have sufficient power with the 20pin connector.