Q: what problems can you get if you use a under power power supply for a graphics card? example 230 watts psu 300 watts required graphics card
A: I already told you why... The video card will underclock itself to not use as much energy, which will kill its performance. It also will run the power supply at maximum load all the time which could lead to power supply failure or also could make the power supply damage other components if the ripple and noise gets to be too high. In other words...it's not a good idea to do.