I have a quetion - I am going to get AMD phenom II x4 probably 2.8Ghz , and GF5615-p33 maotherboard = but - will 300W psu gonna do well ? + I might get V-Card too HD 4550 , that needs 300w PSu .... + 1 Gb of ddr 3 ram
So how will it go ?? 300w Psu isnt good but , how will it go ?
These are the official recommended power requirements based on your graphics card:
300 Watt or greater power supply (350 Watt for ATI CrossFireX™ technology in dual mode) is recommended.
This applies to the entire system not just your graphics card.
Recommended brands are Corsair, Seasonic and the newer Antec models.
If you go with the 4550 that you mentioned then a quality 300W PSU will be adequate. If you choose a different GPU then you'll have to adapt your PSU to suit since the GPU is often the most power-hungry component in modern systems.
The PSUs I would recommend are the Antec Earthwatts 380W or the Corsair CX400. Both are very solid PSUs and will be able to deliver your required power with ease. If you're unsure about whether you will upgrade in the future and wish to keep the same PSU then obviously it is advised that you go for a higher wattage PSU now to save money in the future. The Corsair VX450 or VX550 would be recommended in this instance.