Some GTS 450's require extra power. Some, apparently, do not. Unless someone is personally familiar with that brand and model - without looking at the card to see if there is a power connector, we can't tell you.
You bought it. Why don't you look at the card to see if there is a power cable connector? It will be a rectangle connector with 2 rows of 3 holes, or 2 rows of 4 holes. Then you will know if it needs a power cable or not.