How many pedals are you planning to use?

You need to check the total current draw. If you google each pedal in turn you should find this in miliamps. You need a power supply with a higher spec than the total of your pedals.

If for example your pedals add up to 5amps and your power supply is 10 amps, you'll be fine. If the power supply cannot handle it, it can burn out or add noise to your rig.

If you are using an fx loop on your amp you can get noise by running all the pedals off the same power supply. This is due to intefering ground noise from different sections of your amplifier. If this is the case, best bet is to use 2 seperate power supplies (one for the front end and one for the fx loop) or get a power supply such as the 'Voodoo Lab Pedal Power Plus' which has isolated outputs.

Don't necessarily go for more expensive = better. After months of debugging, I tried lots of different supplies and solutions, and ended up settling on 2x£20 Boss wall warts and my rig is the quietest it has ever been having previously trying 2 Diago powerstations.
The milliamp`s/Volts are important.Take a look at some R/C Shops....might interesting stuff there,a friend has build a pedal "power plant" with gear from R/C Cars.....
R/C cars? Nice haha.

Well i'm using a Boss DD-20, a TU-3 and a FV500 volume pedal.
I'm a little confused about how to add up the amount of amps I would need to power these?

Would the Harley Benton be enough for these do you think? Or should I go with the twin wall warts?
Get yourself a 1-Spot or a Godlyke Power-all. Either of those will be plenty for what you need, and won't cost you the Earth.
With only 3 pedals mate (and I believe the FV500 is passive) you'll be fine with pretty much anything mate