what kind of laptop power adapter do i need to buy ?

about 2 old age ago i brought a laptop.
Advent and i think the number is 6441 though i cant find the freedom musician all for it on the web .
i need a new charger/adapter with a UK fuse but i don't have the old one so i don't know what sort i need to buy.

The label on the back of my laptop says
Advent 6441

Intel@Pentium@Dual-core T3200 2.00GHz 4096MB 160 GB Blu-Ray ROM/
DVD+/-RW Li-ion Microsoft@Windows Vista@Home Premium 17"Widescreen TFT

F71IL1 DC Input: 20V -- 4.5A

present , i found the laptop online so i think the number is exact. so it is a 6441 Advent.
link :
http://reviews.cnet.co.uk/laptops/advent-6441-review-49300601/

http://www.uktsupport.co.uk/advent/laptop/6441.htm


but former i started looking for an arranger all of them have different inputs and outputs and im uptight it wont work or that it will break my laptop.
here are some examples of the ones i pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item415327ed24

http://www.laptop-power.monoxide.uk/laptop-chargers/advent/advent/series-6000/model-6441.html?gclid=CIvOrLuz6aYCFQUTfAodPQd36Q

i don't know provided what the input and the output should metal.
anyone ?

im asking you again because last incident i got 2 severely controversial answers and i do not want to ruin my laptop.
please aid.