What will happen if I won't provide enough power to a gpu

[blurrperceptor69]

This question popped into my mind a few days ago. Say we have a PC where the usage of wattage by PSU is almost max (total 450, used 420/430).
Now I decide to add a GPU which need around 75 watt but no cables from psu needed (can take required power from motherboard).
Since, the power supply can not provide it with enough power, what will happen? Will it at least show up in device manager?

 

[madmatt30]

Any pc with a bus powered gpu card in wont be anywhere near 450w usage wise

Even something like an old fx 9590 (the most power hungry cpu ever created) would still only be around 300w max load .

So practically speaking your scenario will never happen.

Theoretically ?? Using a underpowered psu & overloadimg it with more wattages worth of components than it can handle ??

If its a quality psu then it will simply shutdown due to overload protection circuitry.
A bad quality psu ?? Could simply pop or catch fire & would likely damage one or more components when it does so.

 

[geofelt]

If a psu can not deliver sufficient power to a gpu, I would expect that the gpu would display artifacts under load.
It might run ok on a desktop, where the load is less, but not on a game.

A gpu using pcie power only will consume a max of 75w.