Bear in mind that the GPU itself will likely be fan driven however. If your primary needs are photoshop centred, you aren't really buying with that in mind.
The UHD is very entry level for PS GPU work. It's not really a GPU because it sits next to the CPU eating up all the heat so can't do much, plus it doesn't have it's own memory. Has quick sync which is good for video render but that's it.
Instead of buying a new Dell, you're better off spending the big ones on a 1060 and a bequiet PSU. It'll take an hour to put in tops, and you're covered on warranty if you don't get rid of the original parts. I'd recommend a 600W+ PSU, but get a 700 so you know it's good for years even if the capacity drops.
https://www.youtube.com/watch?v=-exSelC1lBE <- PSU swap
https://www.scan.co.uk/products/700w-be-quiet!-pure-power-10-80-plus-silver-fully-wired-sli-crossfire-dual-rail-56a-plus12v-120mm-fa <- Bequiet PSU. Silent due to grooved fans that don't really ever turn on anyway. Your dell is cheap because it skimps on PSU so any branded unit will be better if it appears expensive. You need to make sure it has 2x 6pin connectors for the discrete card, but if you don't have them listed in the connections on your PSU a 2xMolex to 6pin adapter is pennies. Bear it in mind if you get another PSU though.
https://www.scan.co.uk/products/evga-geforce-gtx-1060-gaming-acx-30-6gb-gddr5-vr-ready-graphics-card-1280-core-1506mhz-gpu-1708mhz-b <- 1060 6GB. This is a very powerful card, that will give you 6GB of GDDR for Photoshop to work with through CUDA etc. It literally won't matter how fast the rest of your system is, PS will fly with this installed and OpenCL/Cuda enabled. It games pretty great too, and because it's cooling is made for constant work, the burst work demands of your application means it will 99% of the time have it's own fans turned off.
Total price GBP300 to turn your existing system into one that will eat your new Dell alive. You could probably get the new six core in that box. Anything ending in a 50 or higher will be an upgrade to that UHD. Even an older £20 550ti would help.