They are mostly just scam. Any properly designed USB interface would be able to deliver correct data stream to DACs.
If the USB interface design is broken (such as the case of Raspberry Pi before version 4), having a perfect PSU most likely won't solve the problem.
Checksum is usually calculated for your USB device's data transmission. If there's an analog issue when transmitting digital data, you can clearly see the sum is wrong (see the RME ADI-2 Pro FS R BE manual chapter 24.1). Just rest and don't worry about the PSU, until you see such error in your real life.
RME's bit perfect test is different from what you understand it does. You are talking reliability, that is, sending correct data stream in the long run (ranging from minutes to hours) with no transmission error (for instance, a 0 is accidentally recognized as 1, or half of a USB packet is dropped and become 0s.). RME's bit test is for you to test your pipeline (software, OS system, hardware connection) is bit perfect (no conversion such as resampling, bit depth truncation, or mixing is done). They are very different things.
Broken USB cables, interference, or even cosmos radiation, could result data corruption (such as a 0 accidentally flips into a 1). If you use the wrong/broken PSU, such corruption may happen in theory as well. In that situation your system will malfunction (unable to boot correctly for instance. or on Raspberry Pi you'll see a undervoltage sign appear on screen) in the first place. In reality no one need to worry about it until the checksum is wrong.