I have a preamp which came with a wall wart causing hum. Doing
research into past posts here brought a comparison between RS wall
warts back in 1998, saying that catalog # 273-1662 was unregulated and
caused hum while #273-1664 was regulated and did not. Having just
checked RS's website, 273-1664 is no longer available, but 273-1662 is
listed as being regulated (perhaps upgraded over time?).
The power requirement of my preamp is 12 to 13.8 VDC @ 100mA. RS
carries 3 regulated warts which would cover that:

273-1680 3-12 VDC @ 1000mA

273-1662 1.5-12 VDC @ 300 mA

273-1667 3-12 VDC @ 800 mA

Which one would be the best choice to see if I get any improvement?