hi i want to get a gtx 650 and i want to know what kind i should get my spec is amd Athlon 64 x 2 2.5ghz, 3gb ram ,300w psu 500gb i know i have to upgrade my psu
To understand power consumption you need more than just the overall wattage.
You need to know how much of that total can be used on the 12 volt rail(s) since they take the largest loads in a modern system.
After this you need to know how much power your parts will take.
The sub 50 watt number that Techpowerup lists seems quite accurate to me(the card you post(Galaxy GeForce GTX 650 GC) does seem to have a 6 pin pci-e connector from the newegg images.). A gtx 650(non ti and non ti boost) is not a power hungry card.
What X2 cpu model is it since some take less power than others and also please check the power supply for its 12 volt rating as you can get a 300 watt power supply anything from 14-24 amps(168-228 watts) @ 12 volts. That is quite the range. Also multi rail units have a combined rating for both rails that must not be passed.
Multi rail power supply example image. With a power friendly system this runs a gtx 650 with ease.
specifications
80mm internal fan
Built-in power status LED
AC Input (47-63Hz): 100-127V/8A / 200-240V/4A switch selectable
DC Output: +5V/25A, +12V/19A, +3.3V/18A, -12V/0.8A, +5VSB/2A
+5V & +3.3V Shall Not Exceed 175W
+5V & +12V Shall Not Exceed 268W
Approvals UL, CSA C22.2. IEC, EN
This leaves you with 228 watts @ 12 volts(3 amps or 36 watts under the other 300 watt label I posted).
HP boards tend to be rather power efficient because they are very basic. I am also willing to bet they got a good low powered cpu in that thing(based on past hp experience).
Chances are pretty good for you because it is just the base gtx 650 and not the ti or boost model.
so with the spec i showed you and the psu i can buy the gtx 650 and have no problem with it right? I also looked at the asus gtx 650 gddr5 1gb says it only draw 75w
You will have to adjust the settings to get a performance level you can live with. I have not played that game to comment on it's performance on older cpus.