Yes but speeds are effected.
Thats the connector you are looking for. The one on the right is a converter for a standard molex 4-pin to a PCI-E 6-pin. GPU's usually come with them.
But all things considered, that computer is pretty old and slow, and popping a new GPU in it is not going to help your case. You should look into a new computer instead of messing with that one.
300W isn't enough for it I think.
Click the 'Thanks' button at the bottom right if I helped you in some way or if you're a good person looking to thank me for no reason
My high speed fiber optic internet