Any possible upgrades to my x51 R2?

Recently, the NVIDIA GeForce GTX 760 Ti OEM graphics card I had in my Alienware x51 R2 quit on me, so I'm looking to replace the card.

After a little research, I found that the PSU provided is already under-powered as it is at 330W, and many of the alternative cards I am looking at require a stronger PSU.

I do not know what kind of motherboard my unit has, and I'm unsure of how I might go about being able to upgrade the PSU. I've heard some people say that the custom 330W is as strong as you can go. I'd really like to know if this is true or not. (I know that the R1 was limited to 330W, but could not find an answer related to the R2.)

Worst case scenario, could someone point me in the right direction to replace my GTX 760 Ti with an equal power card. It did well for what I needed, and I'm unsure of if I could get my hands on the same card, since the OEM is apparently a custom card that can't be bought on the market.

Thank you for your time and your experience. I'm really quite lost when it comes to the finer details of computer customization, which is why I got a pre-built system to begin with.