My graphics card may have failed recently. When I tried starting the PC with the card installed, the system repeatedly powered on and shut off with a clicking sound. The computer boots normally when using the motherboard's video output instead. I currently have an i7-4790K, a 600W Apevia ATX-PR600W power supply, and was considering replacing the card with a GTX 1080 Ti. Could the existing PCIe power cables damage the replacement GPU, or should I replace the entire PSU first?
3 Answers
A new PSU normally comes with its own cables, but only use the cables supplied with that specific PSU. Modular PSU cables are not universally wired the same way, so never reuse the old modular cables even if the plugs fit. If the old PSU is non-modular, its permanently attached cables obviously cannot be transferred.
A power supply that repeatedly clicks and shuts the system down may be triggering its protection circuitry because of a short or failing component. The GPU could be the problem, but the PSU should be treated as suspect too. Replace it before testing a new card, and make sure the new PSU has the required PCIe connectors.
The exact PSU model matters more than the wattage alone. Since that Apevia unit is likely around a decade old and is a budget model, I wouldn’t risk connecting an expensive replacement GPU to it. Replace it with a reputable 650W unit at minimum; 750W gives you more headroom for a 1080 Ti and future upgrades.

Would I need to buy the power cables separately, or do replacement PSUs normally include them?