Noisy Fan may be simply a dry bearing -
This is simply remedied with a drop of light oil on the bearing - under a silver foil label on the boss of the fan.
The speeding/up down is normal as the PSU comes under increasing/decreasing load.
PSU's are pretty standard and simply replace it with one of similar out put or higher- they come now days with a adaptable MoBo power plug to cover different boards types simply put in what came out.
As for suppliers they are all there on the Web
to name but three
For a machine like the E Machine you will not need a horrendously expensive one- just browse and take your time.