When I worked at an eltronics recycling center (we repaired and resold PCs and printers) we used isopropyl alcohol in spray bottles to clean pc parts. It worked really well. Don't dunk anything! Just carefully disassemble, spray the part (let the run off fall onto a collection pad), and let it completely dry before reassembly. It may take a few rounds depending on how dirty the part is, resist any temptation to scrub off build up on electrical components. If contaminates absolutely will not come off use a circuit board cleaning "paint brush" with circuit board pcb cleaner to gently clear it or better yet, leave it be. The enemy of good is perfect.
WARNINGS: Wear gloves, eye protection, and a mask. Follow all ESD safety protocols to protect computer parts. If you disassemble the cpu add more thermal paste. DON'T SPRAY THE PSU, if necessary use alcohol on a wash cloth for the PSU exterior. You can speed up dry time by air blowing excess liquid off but be aware this may splatter dirty droplets around the space. Only clean your PC like this in a well ventilated space. Only attempt this if you are comfortable disassembling and reassembling your pc. However long YOU think your computer needs to be fully dry, double that time to be safe.
Also as a bonus. You can put non electric components in the dishwasher. No soap, no heat, as long as they fit and won't get dinged up by moving dishwasher parts. SERIOUSLY DO NOT HEAT DRY OR WASH ON HIGH HEAT.
I also throw my mechanical keyboards in there but there's always a chance they won't work after - so far tho it's been a success (obviously I make sure they are fully dry before I use them . If you attempt this - at your own risk.
That's true. I usually don't suggest it because when I worked on desktops I developed a philosophy with PSUs of leave them alone if they work and replace them if they don't. In my experience PSUs are extremely tough, and even in the worst conditions rarely failed. It caused more harm then good to mess with them unnecessary.