I am just wondering if the dust filter is restricting air flow to the PSU or not. Its a really bad brand "Xeon" I believe
I doubt that the dust filter has any effect, assuming it is not clogged.
It would be better to replace a cheap psu. It is not uncommon for a bad psu to not deliver it's advertised amps on the +12v rails where it is needed.
What is your graphics card, and how many +12v amps does the data plate on your psu claim?