Would you replace a 10-year-old PSU for a new build?

I’d replace it. A good unit can last a long time, but ten years is already a solid run, and a new PSU removes one aging part from a new build. It’s a precaution, not because the motherboard and CPU upgrade automatically make the old one unsafe.

If you do swap it, use the cables supplied with the new PSU. Modular cables aren’t universally interchangeable, even between units from the same brand.

If it’s been stable, is in good condition, and you’re keeping the same graphics card, I wouldn’t treat its age alone as an urgent reason to replace it. Changing the CPU and motherboard doesn’t by itself call for a different PSU, and 850W may be ample depending on the rest of the system.

There’s no simple test that can promise how much life a PSU has left, though. If avoiding a possible future troubleshooting headache is worth the cost, replacing it is a reasonable choice too.

The graphics card is the part I’d check before deciding. A future GPU upgrade can change the power requirement, connector needs, and transient load, so check the specific card’s recommendations rather than relying only on the current wattage estimate.

For the CPU and motherboard change alone, keeping the PSU is defensible if it remains stable. Replacing it now is also a sensible bit of prevention after a decade. I wouldn’t buy a cheap tester expecting it to predict remaining lifespan; it can only give a limited check of the unit at that moment.