upgraded my dell g5 5000 with 3070ti

It might be worth checking other settings like monitor/screen resolution, what kind of CPU is running on another PC, his RAM and speed of disk drive, then probably how well operating system was configured and what other processes are running on a background.

What PSU did you upgrade to?  Brand and watts?  Also, did you have to get special cables to connect it to the motherboard? I have a 500w PSU now but want to upgrade to a 700w or 750w to fit in a 3070 card.

If you have the 500w PSU you can upgrade to the 3070 no problem. I would be suspect using a 3070 ti as they TDP at 290W. The bigger problem is power connector type and the size of the card.

I recently upgraded to an ASUS 4070 Dual OC. It fits and works perfectly, however there are two large buts: The length (267mm or 10.5") is the absolute maximum you can make fit in the G5 without modification (but even then, I had to bend the back of the case out to get the slot bracket to clear the case) and the power connector is very close to the case panel once it's plugged in. Some users have removed the 3.5" drive bracket from the front but I have a spinner in that spot. The three-fan full length cards will absolutely not fit this case.

The 4070 pulls 200W (and therefore most will use 8pin power, however the founders editions do not) but even under full GPU load doesn't cause instability or crashes.