Which power supply?

Hey

I just bought the "ZOTAC GeForce GTX 550 Ti AMP! Edition". Its product page is

http://www.zotac.com/index.php?page=shop.product_detail...

The package includes a DC power cable which connects between the card and the system power supply unit.
The cable is a "Dual MOLEX-to-6-pin PCIe power cable". It looks like this (random google image):

http://func.de/img/p/06759_o.jpg

Now the thing is I'm lacking the dual 6 pin thingy on my power supply... so obviously I'll have to buy a new power supply but I'm not sure what's important and it shouldn't be too expensive (should be less than 100€).

I need a power supply with 400-500 watts (must be AT VERY LEAST 400 watts) that provides my hardware with power. My computer has the following stuff in it:
- AMD Phenom II Quad 955 4x3200 Mhz
- ASUS M4N68T-M LE mainboard
- 8gb of ram (2 x 4096mb)
- 1000gb s-ata hard drive
- 22x LG Dual Layer DVD +/- R/RW DVD burner
- zotac geforce 550 gtx ti amp! edition (my current graphics card is the radeon hd 5450)

My current power supply is: 420W LC power 420H silent deluce atx power supply
It has 420 watts but is lacking plugs as I already mentioned above.

I have already searched for power supplies. What do you think about this one?
http://www.xilence.net/gr/produkte/power-supplies/red-w...
It's 50 Euros on amazon but I don't know whether it has the plugs I need.
Or maybe this one for 60 Euros?
http://www.amazon.de/quiet-Pure-Power-Netzteil-530W/dp/...

I have read on some forum that it should have at least 18 Amperes on the +12V rail but I honestly don't know what all that means I'm a complete noob

I don't know, I don't know...

Can you give me your opinions on this please? I'd greatly appreciate any help!
Also sorry for my poor English - it's not my mother tongue. I tried my best.

Thank you so much