Dell Dimension C521 - Manual (Page 45)

DC Power Connector P2
DC Power Connector P3
DC Power Connector P4
DC Power Connector P5 and P6
23 VCC (+5V) Red
24 GND Black
*Use 22-AWG wire instead of 18-AWG wire.
Pin Number Signal Name 18-AWG Wire
1 COM Black
2 COM Black
3 +12 VDC Yellow
4 +12 VDC Yellow
Pin Number Signal name 18-AWG Wire
1 +12VDC Yellow
2 COM Black
3 COM Black
4 +5 VDC Red
Pin Number Signal Name 22-AWG Wire
1 +5 VCD Red
2 COM Black
3 COM Black
4 +12 VDC Yellow
Pin Number Signal name 18-AWG Wire
1 +3.3 VDC Orange
2 COM Black