First of all, Happy new year!
If you're just after good sound for little money (not perfect, and not like it could be achieved eiither), I wouldn't go listening to hifists nor electricians. Just try with whatever psu you got what it sounds like. As long as you make sure the voltage doesn't go over the mentioned 24v. Tip: one way to make a poor man's "regulated" powersupply is to add some resistors in parallel to the psu dropping the voltage to acceptable levels and reducing fluctuations. The voltage shouldn't fluctuate more than 1% on a proper psu which *should* be hardly noticable when listening.
As for switching powersupplies and sin and tan noise patterns, .. It's as simple as noticing they are there, and if it bothers you, get a better psu. Other than the additional noise, it shouldn't affect the sound quality. Once again *shouldn't*, like most things in hifi world, things are very "iffy".
Well it's around 8am here and I've yet to get any sleep, and to be quite frank, getting up from this chair won't be as easy as typing with keyboard either.
I suppose it's around midnight in the us, so have a smashing time and happy new year!