first of all can you upgrade your PSU to at least 350-400W? and secondly, for 100$ radeon HD 7750 is a great card and does not require a aux. power connector as it consumes about 55 watts at max load. so that leaves about 200 watt for the CPU and other things. if your CPU isn't a really power hungry one, and if your PSU is not a generic one then you might be able to manage the 7750.
but nonetheless i recommend upgrading to atleast 400W in the near future to stay in safe zone.