Since Google only brought up 2 pages of results and none othe them included the specs of this PSU: AGI HP-W4307F3, I belive it would be safe to say that this is unfortunatly a bargain basment model and it would be very likely that it consists of lower quality parts and can not be trusted to delived the rated amount of power.
It would suggest if you can get a new PSU to do so just for the safety and to give your new parts a good reliable/clean power source.
You probably only need about 350w-450w PSU, use this tool Antec Power Supply Calculator
and put in your PC specs to get a good estimate on how much power your PSU wil need, I gave a large estimate just to cover all the bases and to be safe, most PC that do not have high end graphics cards really use far less power than you would think and even ones with newest most powerfull GFX cards in Crossfire or SLI use below 700w.
With that said I would recommend and Seasonic, Corsair, or Antec PSU for a good replacement. Here are a few good choices for you to take a look at:Newegg.com - 5 good PSU'sNewegg.com - 2 More good PSU's
I hope that helps you out, All the PSU's I listed should work for you perfectly and they are all top quality brands, you just need to see what is in your budget, consider if you are going to upgrade you GPU, and if you want to buy a 80+ certified for better power efficency.