Not sure how many watt your 780ti draws. I had 780 it it was abit over 250watt. Am guessing a 780ti model use abit more. Near 300watt on max power draw.
So i take it yoru card has 2x 8pin connector. 1x 8 pin stands for 150w and your PCE slot provide 75watt.
means you only provide a maximum wattage of 225 to your card. In the end your card will demand 250plus watt and will strain your pci slot and 1x 8 pin. I guess you can imagine what wil happen. Risk to burnout your PCI slot/Powersupplie.
But a power regulater is easy to replace. Also kinda curious how this could have happend