Ok so based on those answers I am going to suggest that you pick up a GTX750Ti without PCIE connectors. It'll work with your 300W PSU and is a good match for your A10.
The 02G-P4-3753-KR (EVGA 750Ti ITX) is $129.99 @ Newegg and $124.99 at NCIXUS online. If you live near a microcenter you may be able to snag it cheaper.
The reason I suggest this GPU is that it works well with very low end power supplies. It is designed for integration into low end OEM systems like what you have, and the power it provides in terms of raw performance is a good match for an A10.
EVGA is probably the best brand you could buy a GPU from and they absolutely have your back if you have a problem with it, unlike, say, ASUS.