Dell Optiplex 740 Motherboard Diagram -

If you need a visual diagram, search Google Images for "Dell Optiplex 740 boardview" or "Optiplex 740 BRD file" – these are CAD drawings used by repair shops.

Dell uses a proprietary pinout on many Optiplex models of this era. The 740 is known to use a standard voltage layout but a different wire color scheme. However, to be safe, do not use a standard ATX PSU without an adapter. If you must test, here is the Dell pinout (measured from the clip side of the connector): Dell Optiplex 740 Motherboard Diagram

Understanding the layout helps you upgrade wisely. If you need a visual diagram, search Google