Power supply keeps restarting when operating

My PC keeps restarting when I am working, its a pain cos I often lose work. I am offgrid and run a small generator for the computer, (thru a filter to protect from power spikes).

Previously the powerpack would make strange noises, a biit like there was a lot of dust build up, but I did manage to blow it thru to clear it out, however, now, even though its running quieter the random restarts are becoming frustrating, sometimes when its powering up it just restarts...I know I can replace the power supply but would rather save the cash and try to fix it myself, if I fail I can always go get another power supply I suppose. Any suggestions?