Use a PSU calculator for the parts you’re selecting. Power supplies are rated to always provide consistent load of at least 80% of rated spec, so aim for a PSU with at least 20% overhead. So if the system uses 600w peak, you’ll want a 720w PSU or better.

In general, an 800w PSU is generally more than enough for most systems, unless you’re buying really power hungry parts (think Nvidia 5080 or 5090 and the highest end Intel chips or AMD threadrippers).

If in doubt, just buy a bigger PSU than you need, like 1000w. Always better to have more than you need, it only uses what the system requires, it’s not like it’s always actually going to draw that 1kw power.