I'm planning a fairly standard RTX 5080 build with a liquid cooler and regular fans. Is a good 850W power supply enough, or should I go with 1000W?
The house has an older electrical system, so power use is a concern. I don't plan on upgrading the build gradually.
For a typical build, a good 850W unit should be enough. Nvidia recommends 850W for the RTX 5080, though the rest of the parts matter too. A very power hungry CPU, especially with overclocking, could make 1000W worth considering.
Check the estimated draw for the complete parts list, then leave some headroom rather than choosing a PSU right at the estimate. Quality matters more than just the number on the box.
A 1000W PSU doesn't force the PC to use 1000W. The computer draws what it needs for the task, and the PSU pulls a bit extra from the wall because conversion isn't perfectly efficient.
So buying 850W instead of 1000W won't necessarily reduce the load on your house wiring. Compare the efficiency of the specific units if wall draw is a concern.
I'd look for a well reviewed ATX 3.1 unit with a native 12V-2x6 cable for the card. Check the connector and cable rating on the particular model, rather than assuming every 850W unit has the same setup.
Modern ATX power supplies are designed to handle brief power excursions, but that doesn't make every model equally good. Independent reviews can tell you more than the brand name alone.
The old wiring is a separate issue from PSU sizing. A quality power supply or a line interactive UPS can help with some power problems, but neither fixes unsafe wiring or an overloaded circuit. If the electrical system is questionable, have an electrician check it before relying on the new PC.
-somewhat-sideways:
Also consider what else shares the circuit. The PC isn't necessarily the only load the wiring and breaker have to handle.
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l8.portcfg:
The exact CPU would help narrow this down. The cooler and standard fans are unlikely to be the deciding factor compared with the CPU and GPU.