You need to be keenly aware of your specs. From that you determine what can be upgraded. Since, this is relatively a new PC, the products out there *should* fall into place w/o special consideration. I suggest you remove the current PSU, take it to a local store/shop and ask for a 500W or better PSU. A brand name helps here as well. -OR- But, you can also research what the new video card and anything else you install requires in wattage, add it up and then add 100W to it or better a PSU that far exceeds that. If you have to, "physically measure" the PSU and any other location of space limitations, etc.. That sometimes is the real way to be sure. Locate(google) the items you plan to purchase and review the specs for the physical dimensions to compare. The process is cumbersome and very easy to do but anyone can do it.
Okay, so I want to upgrade my computers RAM, Graphics Card, And power supply.