Ditto here too on the PSU.. I went to a 850Watt Modular- (Plug in cabling you need for your devices: board, drives, GPU etc etc.). Just have an eye on that Power Supply - check your existing cause you may not have the required power cabling for the 1080IT. That GPU takes a total of two 8-pin connections (16 pin connectors in total) - which equates to:
either TWO 8-pin cables (or 8-pin cable made up of one 6 pin connector plus a 2 pin connector)
and you need two sets of these to hook to the power connections. ors
On the top of the 1080 TI GPU there is a 8 pin plugin socket and another 8-pin socket right beside it.. ALL have to be connected to power it: (and there is only one way the plug-ins fit): (So this is usually two cables from your power supply unit (each power cable from the psu needs to have equivalent of two 8 socket plug-in. (Each one having 6pin and 2 pin)-and you need two sets of them.
(So you can check your 650 PSU but have some doubts that it will have enough cabling of your existing psu to hook into your 1080TI to power it). (Hence why had no choice to upgrade my PSU when I upgraded my GPU cause I didn't have the correct power cabling required. ). I guess should have mentioned that before!.
My new modular 850w psu has ability to plug in 3 sets of cables for the GPU(s) (Max two as I only have two PCI-E slows on my mother board). Anyways, Two power cables from the power supply, each with (6+2 connectors) go to the 2070 and one 6+2 connector cable hooks to the 970.
In your case you need equivalent of 16 pin connector to plug into the 1080TI. So better take a peek at your power supply unit to see if you have the correct or enough power cables for that GPU.
Pic of the 1080 TI power connections belowL (And I think that no matter which 1080 TI you get, all have the same power connections.
Norm