Wanting to buy a desktop than can run Sims 4 and all expansions on high with eas

@thiswebsitesux  Thanks for the dxdiag.  Whether I would personally recommend upgrading this computer depends on its power supply, although you may come to a different conclusion.  The processor should be able to handle Sims 4 on high settings, maybe ultra, but looking at the benchmarks, I'm not convinced that ultra is a reasonable expectation.  You'd also see more slowdowns, or more severe ones, than you would with a newer CPU.  But how much that affects someone's enjoyment of the game varies greatly from person to person.  The RAM and storage are good enough.

With an adequate PSU, you could drop a decent used graphics card into this computer, something that would run Sims 4 on ultra settings (if the CPU can keep up) and that you could probably find on Ebay for around $150.  If the power supply isn't enough to handle the load, you'd need to get a new one (maybe $80) but also re-wire the power cables, which is simple if you know what you're doing... but if not and you'd need to pay someone else to do it, that might cost another $100, give or take, at a local shop.

The other relevant questions here are how long you want to keep this system before upgrading and how long you can reasonably expect it to hold up.  Motherboards start failing after about six years, but they can also last for a decade or longer.  (A new board for this system could still be cheap, in the $60 range, but at that point you're rebuilding the entire computer.)  The processor in this computer is over five years old, although that doesn't mean that the other hardware is that old or that it's been in use that long.  So in terms of how long this will last, it's really difficult to say.

If you'd want to upgrade in a couple of years regardless, then things become easier: spending $150 for a used graphics card now is probably worth it, and spending twice that to also add a new PSU and have someone install it is probably not.  Then again, it's not my money, and you may have other things you'd want to do with your computer budget that would make an intermediate cheaper upgrade preferable to buying a new system right now.

So the first thing to do is find out what power supply is in this computer.  The easiest way is to simply look at it: the PSU is where the power cable plugs in.  Look at the side of the unit to find its specs—I'm interested in manufacturer, wattage, and rating, i.e. Corsair 750W 80+ Gold.  Let me know what you have and I'll figure out what graphics cards it could support.

In your position, assuming the PSU is sufficient, what I'd do if I could is borrow a graphics card from a friend and install it, then see how Sims 4 runs.  You might see enough issues that you're still interested in a new system, in which case you'll have found that out before spending any money.  Or you might decide that performance is good enough for your purposes and that buying a used GPU is the way to go.  Either one is a reasonable approach.