You can use these two tools to understand how much wattage your new power supply will need to deliver and which features you'll want--unless you're upgrading to a new, more powerful graphics card that demands a new, more powerful PSU. Keep in mind that there's nothing wrong with buying a power supply that provides more power than you actually need, especially if there's the possibility of further PC component upgrades in your future.
With your new power supply at the ready, insert it into the exact same position that your old power supply occupied. Reuse the screws that held the old power supply in position on the back panel of the case to do the same thing for your new power supply.
Next, you have to connect the internal power cables from your new power supply to the rest of your computer. Plug the 24-pin power connector into your motherboard first, then go for the 4 or 8-pin CPU power connector. Plug in the optical drives, SSDs, and hard drives. Finally plug any required PCI-E power connectors into your graphics card, then double-check all of the plugs to make sure they are securely seated. If you took photos of or labelled the cables on your old power supply, you can now use those as a reference for figuring out how to connect the cables of your new power supply.
Seal your computer's case back, plug everything back in, and power your computer up. Now you've got a PC that's ready to run for years to come without issue--or at least without PSU-related issues.
Buying a boxed, pre-built desktop is a great way to pick up a computer on the cheap. Knowing how to fix simple issues like a dead power supply is an even better way to get the most out of your money and to avoid splurging on a whole new computer.
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