X51 R2, Gaming issue with spec or something more sinister?

Hi Everyone, First of all my spec: Alienware X51 R2 / 16GB Hyper X Fury DDR3 Ram / Standard PSU / Intel i7 - 4790S 3.2Ghz overclocks to 3.9Ghz / 1TB WD blue + 250GB Samsung SSD / Nvidia GTX1050Ti My actual question - some of the more modern sims, for example Tourist Bus Sim, Rail Sim 19, Bus Sim 18 seem to stutter somewhat. but I've seen other people with similar spec have no issues when the graphics are turned down. I have done this - all my graphics are at a reasonable low/med and I've even set to 720p. The only thing left is that i have the 240w power brick and not 330w - would this make a difference? Is my machine underpowered or can you guys help with any other suggestions? Im quite new to this - so please if there is any other posts that i have re done then direct me. Thank you