Replaces power supply P3BF

Hi.
I just replaced the power supply in my old P3BF Asus motherboard

Now, when I start, I get an Hardware monitor found an error, press DEL to
enter setup and check monitor status.

In the voltages section, where it should be -5V it's -6.1V in red.

I tried another power supply and get the same error.

The computer runs fine however if I ignore this error but would like to know
why I get this.

Thanks