Linear power supply design

I'm trying to do a project where I'm creating a linear power supply for a pre-amp of an audio circuit. The main focus on the project is the power supply itself.

I'm needing some help explaining how this circuit works (Attached), mainly why there is use of electrolytic capacitors in parallel to the capacitors. I've altered the circuit to get a 40v output from a 230v input.

Also, how do I add overcurrent and overvoltage protection?

If anyone can break it down into simple terms I would be appreciative, I'm not a huge electronics boffin and this is just a small part of a course.

 

Thanks for taking a look, I'd be wanting to incorporate a varistor within this circuit somewhere.

 

Thanks jc, I did read it was up to 40v, I'm currently getting 20V maximum going across the IC, would this be acceptable?

Thanks for your input duke, I've never seen the two coupled together before, I've just chosen that circuit as a starting point, would reducing the current requirements be easier?

 

I'm actually having a problem at the moment with the fuse randomly blowing, have I got a mistake in the software or is the circuit not right?

 

Thank you all for your input, I've made some good changes. How would I set up overvoltage protection?

 

Can someone please show me how to get overvoltage protection on this circuit? I've tried a few varistors across the supply and after the rectifier, but I still can't get it to switch to ground on overvoltage