I would double check that with multimeter (Cheap 10$ would work).
How old is your thermaltake XP550?(google gives me review from 2008, soo it seems quite and very old).
If you have molex connector (4 pin to connect to fans or old HDD) going Yellow Black black red, you plug probes into red and black (check out guide how to use multimeter if you are not sure).
If it shows 6V, thats quite
HIGH for it. Usually PSU's have to be withn 5% spec, for 5V would be 0.25 up and down.
It might be the 5VSB (or known as stand by voltage, which comes into play when PC is not powered on but plugged into power and usb ports provide voltage up to 1-2A, depending from PSU manufacturer).
In end I would suggest you PSU swap before that PSU fries something on motherboard.
Power Supply Voltage Tolerances (ATX v2.2)
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Voltage Rail | Tolerance | Minimum Voltage | Maximum Voltage |
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PSU Tolerance Table | | | |
---|
+3.3VDC | ± 5% | +3.135 VDC | +3.465 VDC |
+5VDC | ± 5% | +4.750 VDC | +5.250 VDC |
+5VSB | ± 5% | +4.750 VDC | +5.250 VDC |
-5VDC (if used) | ± 10% | -4.500 VDC | -5.500 VDC |
+12VDC | ± 5% | +11.400 VDC | +12.600 VDC |
-12VDC | ± 10% | -10.800 VDC | - 13.200 VDC |