Mostly sounds like culprit is 3080, but you could check how he connected 3080 (preferably individual cables from PSU to GPU), and if you tried with a low power GPU, could it possibly be that there is something wrong with PSU and it can't deliver enought power to 3080. So most likely 3080 problem, but if easy, would probably check power related issues. Just remember, you can't use power cables of one PSU with another PSU as wiring isn't necessarily the same. So if you try with your PSU, change cables too.