Yes, it is a Dell xps 15/L502X version.  

I'm going to update the BIOS anyway and see.  Kingston asked me to try installing each one separately, I guess to see if they are both good units. 

I followed Kingston's instructions and I now have 16 gb.  I may not have seated one or the other properly.

Hi - can you post the details of the kigston memory you used?  What bios version do you have?

Thanks much

Found it faster than I thought.  Good luck.  I think the key is seating the memory correctly. I think the edge of new memory needs a little working in before it fits right.  Anyway, I got it done.

Link to latest BIOS.

http://www.dell.com/support/home/us/en/04/Drivers/DriversDetails?driverId=0VRMP&fileId=3080904365&osCode=W864&productCode=xps-L502x&languageCode=EN&categoryId=BI 

Here's the link I failed to attach to my post above:

http://superuser.com/questions/81094/4-00gb-3-25gb-usable-in-windows-7-x64

I've just successfully upgraded from 4GB to 16GB RAM, with only one obstacle encountered:

After installing the new RAM, although the BIOS and Windows where acknowledging the presence of the full 16GB, Windows System Information stated only 2.96GB as usable - the same value as when only 4GB of RAM was installed.

Searched for a solution and found this article. I tried this instruction first and it worked:

Open MSCONFIG, select BOOT TAB, click ADVANCED OPTIONS and make sure MAXIMUM MEMORY is UNCHECKED. Apply, OK, restart.

Now Windows System Information indicates 16GB RAM (15.9GB usable).

My System:

L502X XPS 15 with i5 2520M 2.50Ghz

Windows 7 Home Premiuim

BIOS Version A12

Good to know of your problem and solution.   Thanks for sharing.

Thanks everyone! I successfully installed 16GB on my XPS L502 system. Had A12 BIOS versioin already.

This is the memory module I used:

http://www.amazon.com/gp/product/B0089JIDUI/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Does it work with an Intel I5 2430M 2.40GHz ?

Yes, check this page under "Max Memory Size": http://ark.intel.com/products/53450/Intel-Core-i5-2430M-Processor-3M-Cache-up-to-3_00-GHz

I just want to confirm that my XPS L502X works with 16Gb of RAM.

CPU: i5 2401M 

MB: ONJT03 A00

Bios: A12

Memory: 2 X 8GB Kingston DDR3-1600

Thanks for the tip @Rickard505. On the strength of this I ordered 2 x Crucial 8GB PC3L-12800 from RamCity. These SO-DIMM units are rated at 1600Mhz but RamCity say they auto-detect and adjust to clock speed down to 1333Mhz and so far they seem fine.

Hi ,i decide to upgrade my ram to 16 ,i want to no after all this time never had any problem with hitting or something else?