Please ignore this duplicate flag. It's wrong!
Let's say I have the following situation: I have a graphic card which can, with default settings, draw up to 250W from the PSU under full load. However, I don't actually need the maximum performance. I just need the features that come with this card, like a large amount video memory. Thus I will reduce the power limit with software. Most modern GPUs, or at least the GPU I am talking about, do have a power target setting where some sensors inside the graphics card can cap the power usage at this level. You can typically reduce the power by a lot while only sacrificing a bit of performance, as for example reported by this guy.
I know that 250W combined with all other components at maximum power usage will be too much for the PSU. Not by a lot, but still. Let's say it would be totally fine if the GPU drew only 200W from the PSU.
Since I never intend to use the full 250W and will turn the GPU into a <200W card after startup, this should be fine, at least after startup. The only critical phase therefore is the time before the operating system has loaded and applied the software patch that caps the power usage of the card. It's only a temporary fix that will be in place until reboot.
So the question is whether at the moment I turn my PC on (and the software fixes are not yet in place), all components including the GPU will initially draw their maximum power usage from the PSU at the same time and thus will cause the PSU to be overloaded in this instance of time. Or whether the GPU will only draw its maximum power if it is actually busy with a task and thus the PSU will not be overloaded during the startup period.
Please note that I don't want advice in the form of "will this specific PSU be enough for my system", but I want to understand in more detail what challenges the PSU has to deal with, like in the present case about initial startup power usage, so that I can make an educated decision myself.