Well, there’s a good reason for the 24-pin power connector. The +12V supply is where components are shifting to. As this becomes more central to the power provisions, the need to spread the flow out was needed to avoid creating a fire hazard. Part of that included moving from 20-pin to 24-pin connectors, previously seen on server and workstation motherboards.
I don’t know the specs of the 300W you have now, so I couldn’t tell you if it has enough amperage on the +12V for your needs. I run a modern box with 330W unit, but that’s because the +12V has 22A. If I were looking to use it as a gaming rig, I’d want something with at least 25A.
If this is for gaming, you will want to invest in a new power supply. If this is for something more basic, like websurfing, you might be able to get by if the +12V has at least 20A. However, I’m willing to bet it’s not up to that. For a budget, look at FSP/Fortron/Sparkle (same company, different brands) or Ultra units. If you can find them, XClio is also another choice, but they don’t seem to pop up outside the US. Something 450-550W from these brands should be enough unless you’re looking at some uber gaming box with a high-end video card or two.
I really wouldn’t use the 20- to 24-pin adapter. The use of unsoldered contacts increases the resistance, which makes the power supply work harder. Plus, the ATX power connectors are keyed so that you’re not going to be easily able to get it in incorrectly.
[COLOR=“DarkGreen”]But it should be manufactured specified one. Otherwise SMPS is gone. Simply you can find on there official web site. And also those details are labeled on the sticker of any SMPS.