I don't know why most suppliers still provide a Desktop with a 350 Watt power supply. That would be O.K. if you are not upgrading with faster Graphics Cards, more HD Drives etc. I once bought a new Graphics Card (brand name) and just by looking at the thing in the shop prior to reading it's instructions I asked the technician if I should not upgrade the PSU as well to a higher wattage. But he assured me that the current 350 Watt PSU should be sufficient to cater for that Graphics Card as well. At home, I carefully installed the Graphics Card & press the start button, and smoke then became visible from the PSU and it shut down the PC.
Then I took out the Graphics Card manual and I read it...to my surprise (and to the surprise of that technician) the Graphics Card specs shows that it alone draw about as much wattage as what the 350 watt PSU could provide, let alone the Mother Board & the HD Drives. So, back to that shop again and I purchased a 720 Watt PSU and the problem solved.