Upgrading PSU for installing higher graphic card.

Friends,

I have Dell OptiPlex 7090 which came with 260W PSU. I am not a gamer at all.  I am video editor only and I use Vegas Pro, Adobe Premier to creat my music videos that is only the load on the PC.

(1) I installed GTX 1050 ti 3 years ago and it is working normal.

(2) To gain some speed in Video rendering, and to gain access to NVIDIA Studio (to live-stream my music playing with Logitech Webcam C922 Pro) I wish to upgrade my graphics card to gain access to NVIDIA Studio.

(3) I purchased a used RTX 3070ti.

(4) Load on the graphics card will be only video rendering, and just livestreaming in YouTube. 

(5) So, I feel if I purchase from Amazon or any source, a DELL 500 watt, 600 watt or 700 watt psu, I think it will serve my purpose.

(6)My personal opinion, Purchasing a 500watt to 700 watt as available, does not throw a load on the Motherboard because the working load is very nominal, using only for video rendering and livestreaming in YouTube.

(7) My PC is OptiPlex 7090, 64 GB Ram, 64 Processor, 64 bit Operating System.

(7) Please advise me friends any DELL PSUs available in Indian market with the model numbers for 500, 600, 700 watts. Also please advise me if my opinion is wrong anywhere.  Thanks in advance.