I'd like to upgrade the graphics card so I'd be able to have a vga and hdmi output also.
It depends on what you are trying to accomplish. If all you want to do is add a monitor then the adapter route is the way to go. If you don't play games don't waste your money. If you want faster gameplay then getting a more powerfull card is the answer. While the 7750 doesn't require any additional PCIE power cables, you have a 300w power supply in there, which gives you about 200w of headroom (150w) conservatively, all cards that require extra power cables come with adapters for 4 pin molex to pcie. This would put an hd 7850 or a 6870 within your envelope at the upper end. http://www.tomshardware.com/reviews/gaming-graphics-car...
you also have to consider physical size since many high power graphics cards are large and will need a big case in order to fit, measure how much length you have available.
Of course cost will also be a factor for most. Remember that adding a powerful graphics card is likely to make your computer much louder and hotter than before.