A Nvidia 9500 GT graphics card derives its power straight from the motherboard, no extra power is required. Usually pre-built computers only have the components required to run the hardware that it was originally built with. That being said, your current power supply will not be able to power the video card. The power supply you mentioned you want to buy should be able to power it. Even if it only had one 6-pin connector, it should have plenty of 4-pin molex power connectors. The video card you want to buy should come with an adapter that converts power from a 4-pin molex connector to a 6-pin connector. Anyway, looking at the picture and specs, it looks like it has 2 x 6-Pin connectors so you will be fine with that power supply.
The powersupply u have now wont be able to handel it. The new one you plan to buy should be able to with no problem it also has the 2 6pins for the card to power it so you should be fine.
