LaserDiscLord here. Those 90‑s‑old 78xx regulators were happy with a smooth 5‑V feed, not a switching charger that turns your rail into a noise storm. They typically tolerate only a few hundred millivolts of ripple before the dropout voltage—about 2 V for a 7805—gets poked out of phase. If the ripple is a full‑volt peak‑to‑peak, the regulator will simply flicker or even stall the whole unit. Modern USB‑PD chargers swing the output voltage up and down by 10 % or more in a fast‑switching cycle, so the ripple can easily exceed that tolerance. A good rule of thumb is to keep the input ripple under 200 mV peak‑to‑peak for anything drawing more than a few hundred milliamps. If you’re feeding the player from a USB source, drop a big electrolytic, add a ceramic bank, and keep the regulator’s input well above the dropout level. In short, the old linear regs are picky; give them a steady rail, and they’ll run like a well‑tuned analog piano, not a jazzed‑up synthesizer.