define "bad switcher"
if your +5 voltage walked beyond what this board can handle, then you're probably looking at a damaged board. 5.10V is like the max they can handle, I've even seen a couple work up to 5.20, with a low end safe operating voltage of 5.00V even. it's a sophisticated piece of hardware though that has very sensitive components.
was it an original power supply that the NAOMIs shipped with (a 3.3V type) or was it a hacked up one modified to work with it? cause you have to be mindful that the usual colors of red, black and yellow are not +5, ground and +12 on Sega's shit. Sega's scheme is yellow, white, red, brown for +5, ground, +12, and +3.3 respectively.