Gtx 550 compatiability

my configuration>
asus P5QPL-AM
link- http://www.asus.com/Motherboards/Intel_Socket_775/P5QPL...

2 gb ddr2 ram.
pentium dual core clocked at 2.8 ghz.
a powersupply unit of 400 watt.

I want to buy a gtx 550 ti 1gb ddr 5.
now i know that my motherboard supports this card but i have doubts with the PSU! will the exixting one able to hold the wrath of gtx 550 or do i get to need a new one.
If i have to which one should i get?(there are some compatiability issue of psu's in regard to the pins it uses to get connected to the motherboard) keeping that in mind...please help. it will be greatly appreciated.