Your absolutely right. Your PC would quite happily support the card, but you can check your power requirements here:
eXtreme Power Supply Calculator v2.5 (click go lite, and compare the results to how much you currently have. The wattage can sometimes be found at the back of the power supply. But in many cases you may need to remove the case where the wattage can be found on the size or top).
If your out of range, you will have the option of either going for your first choice, or purchasing a new power supply, but I guess that would take you to far out of budget.
EDIT: Marked as answered.