PSU switches off at random times

[Mincus]

I've added a new Seasonic Prime TX-650 to my system and ever since it causes the machine to switch off randomly.
System is Ryzewn 3900X, Geforce RTX 2080 Super, MSI Carbon X570 motherboard. Nothing overclocked.
Machine runs fine on an older (also 650w PSU).

 

First boot it lasted about an hour before switching off, now it does it within seconds.

Even just switching the PSU on with no load, it turns off after a random amount of time from immediately up to ~20 seconds.

 

Is there likely to be a fix or should I just RMA the PSU?

[Haro]

set the power limit to 50% on gpu and try a stress test and see if it crashes 

[Gorilla Warfare]

Most likely a defective unit.

[Mincus]

9 minutes ago, TofuHaroto said:

set the power limit to 50% on gpu and try a stress test and see if it crashes 

Maybe I wasn't clear on this:

It powers off within 20 seconds of powering on. Load makes no difference. If I'm in BIOS, it powers off. If I get to Windows, it powers off.
It even powers off in the same time period if I just short the power pins on the ATX connector.

[Haro]

2 minutes ago, Mincus said:

It even powers off in the same time period if I just short the power pins on the ATX connector

probably a dying unit then like what  @Gorilla Warfare said