There are worse ideas than running a 980ti on a junk PSU plus using 6-pin adapters.
For instance, you could connect your genitals to an electric socket with copper wire. You could run into a police station screaming that you have a bomb. You could dress up like Mary Poppins and see if you can float into the clouds by jumping off a building holding an umbrella.
Those are all the ones I can think of right now. There are probably 2 or 3 other ideas that are worse.
Now, maybe you don't like your new 980ti. Maybe it brutally murdered your family and, knowing that revenge is a dish best served cold, you methodically planned your revenge, gleefully anticipating the day that you could fry it alive, smelling the satisfying stench of burning capacitors as you watch its soul descend to its fate of eternal brimstone. In this case, sure, give it a shot. Teach that 980ti a lesson!