It's a mediocre PSU and only good for office builds without dedicated GPU. That's what's wrong with it.
And that's not all. CX650 is made by CWT and Great Wall and when you buy one, there's
no telling which of the two you'll be getting.
Older models of Corsair CX and CXm series (with green labels) were so bad units that they ended up as low quality units (on-par with current Corsair VS series). Corsair has since improved their CX and CXm line (with gray labels) and now, they are better but not enough to be considered as good quality PSU. Bulk of Seasonic units are either good quality or great quality (depending on the series).
While CX series are cheap, you won't get solid build quality and all Japanese caps as you can get with many Seasonic units. Here's one in-depth review of CX650, the Great Wall version,
link:
https://www.tomshardware.com/reviews/corsair-cx650-power-supply-review
Corsair CX650 does provide some good results but it also provides some bad results. Like hold-up time that is way lower than the ATX standard specifies it to be. CX650 has hold-up time of 8.30 milliseconds while the ATX standard for hold up time is a minimum of 17 milliseconds. For comparison, Seasonic PRIME 650 80+ Titanium (one of the best 650W PSU money can buy) has hold-up time of 30 milliseconds.
And it's just not the hold-up time, there are other, more apparent things that doesn't make it good quality unit. One of them is transient response at +12V and +3.3V. With load changes, PSU is struggling to keep the voltage stable and within ATX standard specs, while at +3.3V rail, it fails to keep voltage within ATX standard. And off-spec voltages mean damage to other components, either frying them on the spot or gradually damaging and shortening components lifespan.
It being fully-wired doesn't help either, since with that, you will have leftover cables that you have to somehow place somewhere. With semi- or fully-modular cables, you only use what you need.
Since CX650 has nice list of good things and also bad things, it's a mediocre quality unit. If there were more bad than good (including price) it would be a bad unit and vice-versa.
I, personally, wouldn't use it. While it can be used just fine for an office PC that never sees any high loads. But for home use in a gaming PC, where PC components longevity is important factor, i'd use and also suggest using better quality PSU.
Different persons have different standards (some have higher standards while others have lower standards) and it's up to every person to decide how good of a build quality components are safe to use in their PC. But keep in mind that PSU is the most important component inside the PC since it powers everything.
Since i care a lot about all my PCs, i won't put a mediocre quality unit into my PC that fails to meet ATX PSU standards set in place for all OEMs to follow, so that the PSUs are safe to use and doesn't damage other components. In fact, i've gone above and beyond regarding PSUs in my PCs.
Some may call me nuts that i payed €206.80 for a PSU that sits in my Skylake build (Seasonic SSR-650TD) and my latest PSU purchase for Haswell build costed €205.50 (Seasonic SSR-650TR), while i would've been safe with a PSU that costs €80.50 (Seasonic GX-550). While that can be true and i could've saved a lot of money, i feel safe and comfortable that my two main PCs are powered by the best offered by Seasonic.
I won't suggest expensive PSUs in builds when the budget is way restricted. But i still suggest getting a PSU that at least meets all the ATX PSU standards, like Seasonic Focus GM-650 linked above.
Focus GM-650 review:
https://www.thefpsreview.com/2021/05/04/seasonic-focus-gm-650-650w-power-supply-review/
Btw, Seasonic Focus GM-650 comes with 7 years of warranty, 2 years more than Corsair CX650.