Good afternoon to all.
My problem is:
I have a Recom PE-450Plus power supply and have to buy a new graphics card to use GPU in cyles.
Have read alot of stuff but my knowledge about this is limited.
My questions:
Is the Recom PE-450Plus power supply enough (does it have the cable connections and power) to connect a GTX 780Ti or a GTX 980Ti?
Is the GTX 780Ti enough memory for Architectural Jobs (Using HDR)?
Thank you very much for your help!
According to this… http://www.geforce.co.uk/hardware/desktop-gpus/geforce-gtx-780-ti/specifications
You’ll need a heftier PSU with added power supply connectors.
I run an MSI GTX750Ti, it gets the power from the Pcie connector, no added requirements and I run it on a 450W PSU, not had any problems, so depends if you want the 780 over the 750, you will have to factor in the cost of a replacement PSU, you’ll want a decent one too, with sufficient overhead in amperage handling.
The TDP of the graphics cards are something you need to look into. I would recommend the latest cards under the GTX 1000 series. They consume very less power under max load. But if your planning for a budget card, the lower end models will tend to consume a bit more power and may require a PSU upgrade as well!
Depending upon your budget, I would say go for a card with a VRAM of 2 gigs atleast and keep an eye on the CUDA count 
Here’s the bench mark link for quite a few cards. You can spot the one you like from performance perspectives!