Zotac GTX 650?

Solution
You should be able to handle it but hp uses terrible psu's, among the worst of all PC manufacturers.

Nvidia recommends 400 watts. Mind you this is always aiming high on nvidia's part. I'd suggest maybe something like a 6450. It should be at least 2 times as fast and have a similar power draw as to what you have. Mind you, the 6450 from AMD does not compare to a 650 in gaming power but you are in a position where a psu upgrade may be required.
You should be able to handle it but hp uses terrible psu's, among the worst of all PC manufacturers.

Nvidia recommends 400 watts. Mind you this is always aiming high on nvidia's part. I'd suggest maybe something like a 6450. It should be at least 2 times as fast and have a similar power draw as to what you have. Mind you, the 6450 from AMD does not compare to a 650 in gaming power but you are in a position where a psu upgrade may be required.
 
Solution