The iFi device is a linear-regulated supply, but it's extremely expensive. HiFimeDIY has a USB isolator that they claim has an improved power supply, but it is not powered externally, so performance can't be dependable. There is an inexpensive DIY solution in the works, but I'd be accused of shilling if I spoke about it in detail. There is information in the DIY section. Another user on Head-Fi - mcandmar built his own device awhile back with proven results. Other than these, I'm not aware of another truly audiophile solution.
Switching power supplies are often very noisy. They claim to have "pushed" the noise well above the audible threshold, but there are many artifacts, phase distortions, etc., that cause harmonics into the audible band. Let me emphasize, however, that "noise" in the power supply is rarely something that's heard. Instead, it's a general lack of quality in sound: maybe a glare in the high-end, a general loss of dynamics, sloppy bass, etc. It simply causes effects that result in sounding blah vs. GREAT. Only extreme examples - not worthy of any consideration at all - result in noise that's directly audible in the sound signal.
Also, switching power supplies can sometimes be used with amplifiers (including headphone amplifiers) with good success. However, every amplifier circuit has a calculated property known as PSRR - Power Supply Rejection Ratio. It's a measure of how much noise in a power supply will affect the amplifier circuit itself. Good circuits have very high PSRR's. However, powering a source such as a DAC does not qualify. Once noise is introduced, it'll propagate throughout the signal stream.
The iFi device is a linear-regulated supply, but it's extremely expensive. HiFimeDIY has a USB isolator that they claim has an improved power supply, but it is not powered externally, so performance can't be dependable. There is an inexpensive DIY solution in the works, but I'd be accused of shilling if I spoke about it in detail. There is information in the DIY section. Another user on Head-Fi - mcandmar built his own device awhile back with proven results. Other than these, I'm not aware of another truly audiophile solution.
Switching power supplies are often very noisy. They claim to have "pushed" the noise well above the audible threshold, but there are many artifacts, phase distortions, etc., that cause harmonics into the audible band. Let me emphasize, however, that "noise" in the power supply is rarely something that's heard. Instead, it's a general lack of quality in sound: maybe a glare in the high-end, a general loss of dynamics, sloppy bass, etc. It simply causes effects that result in sounding blah vs. GREAT. Only extreme examples - not worthy of any consideration at all - result in noise that's directly audible in the sound signal.
Also, switching power supplies can sometimes be used with amplifiers (including headphone amplifiers) with good success. However, every amplifier circuit has a calculated property known as PSRR - Power Supply Rejection Ratio. It's a measure of how much noise in a power supply will affect the amplifier circuit itself. Good circuits have very high PSRR's. However, powering a source such as a DAC does not qualify. Once noise is introduced, it'll propagate throughout the signal stream.