hi techs i need help replacing the power jack on the latitude c640
Do you want to replace the power supply and cord or just the adapter connector? Explain what you want more clearly, thanks...
Be sure to check your power supply FIRST before you try to fix this. They go dead quite frequently.
Power jack = Internet power connector (usually barrel / pin type)
Power jacks are usually soldered onto the system board and require complete system disassembly. The old jack needs to be desoldered (legs are set into the board) and the new one needs to be resoldered in. It's not too tricky if you have at least some skill soldering... But I wouldn't recommend it for a 'first project'. LoL. Luckily it doesn't take a pro, although it helps.
The only way to replace them is to buy one from a place like eBay or a real electronics store. Not all jacks are the same. You need to find one with the same diameter barrel and pin (Or whatever connection is used) and the same legs to ensure it will fit into your board. Some modification may be required after (bending, shaving etc..) to get a good fit.