Question Is my PSU enough?

Jan 31, 2020
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So I'm looking to upgrade my real old pc's GPU and I'm worried that my PSU isn't enough. When I enter my details to a PSU calculator, It says that I need 287 watts. However when I asked a guy he said that my PSU, which is 300 watts rated, would be only able to do 228 watts on 12v rail. (I got no idea what that means) So my question is can I use my ASUS GPS-350AB safely with a Radeon HD 5670?
Just a note: I wasn't able to find a 6pin connector in my case so I got a 2x4 to 6 pin adaptor. I'm going to be powering the GPU with that.
 
Jan 31, 2020
7
1
15
Tbh I'll be getting a completely new pc in a year or two so I don't want to spend a lot of money. Can I use something like a High Power 80+ Bronze 400w?