Upgrading computer for LOTRO

Im having a lot of fun playing LOTRO and recently my video card bit the dust so i'm not getting to experience Middle Earth as it should be.

I found a video card that would run lotro at high settings like a champ and my only concern is it taking up too much energy and my computer only has a 300 watt psu.

Here is the card (notice others have commented saying it works on there 250 watt and 220 watt computers.)
http://www.newegg.com/Product/Produc...-829-_-Product

Here is my pc and keep in mind it has a 300 watt psu and although other people with lower psu's could run the card I could be using up more energy on other components.
http://h10010.www1.hp.com/wwpc/ca/en...-81049107.html

thanks to whoever can answer. :)