84W CPU, 90-100W for the balance + a 75W GPU = 259W.
It would be really close, if new. Given the setup has to be at least 3 years old, that's 3 years of the PSU degrading.
The only way to know 100% would be to try it. Dell's Optiplex PSUs are usually decent-enough that it should work, or it won't. Not likely to damage anything else in the process.