First, let's establish which model you have. What is the service tag number?

Awesome! Thank you! I wonder why the rep told me that I just have the x51 not the R1 or R2 series.

But what about the graphics card that requires 400w minimum that would also work? Because I was looking at the GTX 960.

You have the X51-R1 (1st revision). With your Dell 330w AC adapter, you could upgrade to these Dell validated video cards =
106DK AMD Radeon R9 270 2GB
2CHCY Nvidia GeForce GTX 660Ti 1.5GB

You should read through this thread to find out what other retail video cards might work. It has been reported that these work =

Sapphire AMD Radeon HD 7870 2GB
VisionTek AMD Radeon R9 285 2GB
EVGA Nvidia GeForce GTX 960 4GB

When I talked to the rep via chat and gave them my service tag number and they told me it was just the x51 but not sure.

Awesome, I just bought the EVGA GeForce GTX 960 4 GB. Should I return it and get the PNY one you recommended?

This is what I got thinking about returning it when it arrives and then get the one you recommended?

http://www.newegg.com/Product/Product.aspx?Item=N82E16814487154

The GTX 960, as said earlier, should work fine. I mean, the X51 R2 and R3 can use the GTX 960 with no problems and have a 330w PSU, so the R1 is practically no different for this GPU.

I recommend the PNY GTX 960 4 GB, though. It's cooling design is optimal for the X51 (hot air goes out the case as opposed to in it), and more and more games are requiring a high amount of VRAM, so getting the 4 GB version to the 2 GB version is ideal.

Awesome! 

I just bought this one

Or should I return it when it arrives and get the one you recommended?