Need help identifying this pc's PSU, and if this graphics card is compatible

I've never played videogames before and recently I decided to join the master race. Before I just watched people play games on youtube but that time is over. My parents aren't going to get me anything so I took matters into my own hands and will upgrade my ancient pc (The cheaper alternative to a 400 dollar xbox even tho it will still run like crap).

http://www.asus.com/us/supportonly/CM5571/HelpDesk_Knowledge/

Next link: http://www.newegg.com/Product/Product.aspx?Item=N82E16883220043

The graphics card I found needs a power supply of 300 PSU, here it is: https://www.amazon.com/EVGA-512-P3-1300-LR-GeForce-Express-Graphics/dp/B004BQKQ8A/ref=sr_1_9?s=pc&ie=UTF8&qid=1480720053&sr=1-9&keywords=graphics+card&refinements=p_36%3A1253504011

^The cheapest one on the market. Hands down.

Now I got a few questions:

-Is the graphics card compatible with my computer?

-Does my computer have enough power supply? (I can't upgrade anything else but the graphics card, a new power supply is out of the question. My budget is literally 40 bucks, I'm broke bruh)

-Can it run overwatch? (I'm fine with minimum settings/windowed less than 20 fps, I'm not one of those guys who cries when his 4K moniter displays 119 fps instead of 120. I play minecraft at 9 fps. I was born in the lag. Molded by the lag. I didn't see 720p HD until I was a man.)

Thanks for all your help!

P.S. I was pleasantly surprised by the attention my first 2 posts got on this subreddit. Coming from 9gag, I expected PC masterrace to be rich, elitist, classist scumbags that insult everything, because that's how the masterrace is on 9gag. Here, after 2 posts, countless PMs and 1 reddit gold I have decided that this is the #1 friendliest and nicest community I am subscribed to. You guys rock

Submitted by OgreAggressiveShrek | #Specialdealer Special Offer Online Shopping Store 2016