PSU diagnosing is actually a PITA. Well, not as bad as thermals.
Why? Because EVERY DAMN APP gets "read my data" wrong because "my data" is actually supposed to be scaled by PropretaryAlgorithm(TM) which changes per-chip, and even then, thermals are only valid in certain ranges.
With 5 different motherboard apps, I get FIVE different thermal ratings. And they let you offset them... too bad you don't know what the offset is supposed to be. (And, with my AMD FX-8370, the low range offset is different from the high range offset. So I can either be accurate at low, or high, not both.)
That said, voltages are more likely to be exact, and, if in doubt, you can always get a simple multi-meter and confirm their output (assuming the voltages aren't dropping in short spikes that you can't see).
The point about voltages is, when in BIOS, you'll normally see fine voltages. But the second your computer boots up and gets under load, they may drop. And then you need other a motherboard monitoring app, or, a multimeter.