Did My Power Supply Fail, or Was 850W Not Enough for This PC?

That 850W unit should be plenty for this hardware, so the wattage itself probably wasn’t the issue. A failed component, damaged cable, bad connection, power surge, or faulty outlet is more likely. Don’t reuse the melted cable or power supply, and inspect the wall outlet and plug for heat or discoloration before connecting anything new.

Before installing the replacement, check the entire power path: the PSU inlet, power cable, surge protector or UPS, wall receptacle, and any extension cord. Don’t plug a new unit into a visibly scorched or loose outlet. Also make sure every modular cable comes from the replacement PSU and is not reused from the old one.

Burning plastic isn’t a normal sign of a PSU being undersized. When a supply is overloaded, it usually shuts down or trips its protection circuits rather than melting the AC connector. Since the damage occurred at the rear input, replace both the PSU and cable, avoid that outlet until it’s checked, and contact the manufacturer about a warranty claim.

A quality 850W supply is generally adequate for a 9800X3D and RTX 4080 SUPER system. Moving to 1000W gives you some extra headroom, but it won’t necessarily prevent this kind of failure. The melted connection points more toward a defective unit, damaged cord, loose connection, or problem with the outlet than insufficient wattage.