Right angle 90 degree ATX adapter
Cable management is usually a quite important element of a custom made PC - wherever for good looks or for best airflow or thermal performance. There are custom cables, cases with very good cable management design solutions but usually there is something that may stand out among the cables - arched ATX motherboard power cable. If the bundle of cables won't be flexible enough the arch will be quite big. Solution - right angle (or 90 degree) ATX connector-adapter.
This is a simple adapter that flips the ATX socket by 90 degrees. In the model I have the socket is flipped to the latch side (there may be ones flipping in the opposite side). With two such adapters you can flip the socket to be bottom facing next to the board - which could be handy in cases with cable management cut-out exactly at the edge of the motherboard.
Such adapters allow saving on cable length as you avoid the arching as well as makes the ATX cable less visible in the overall view of the PC. Very flexible custom cables may give similar effect if you manage to get them. Also when the cable is bent it will apply some force to the motherboard and it ATX socket - which is rather good to avoid.
I got my adapter from ebay here in EU, but there are other shops offering them (although not many as it's rather quite
unexpected item?). I've found one on mnpctech.com as well as plentiful offerings on Aliexpress.
Update on the look and color: adapter I got is quite crude looking and green PCB can be seen, but the other model is fully black, where as Cooler Master has an even prettier one.