If the 5V power in your console is flaky or missing, you may need a new regulator.

Many consoles use the venerable 7805 linear voltage regulator to provide a stable and very clean 5V power rail for their internal circuitry. Over time and from often being run pretty hard (such as the Commodore 64’s near 100% duty load) these regulators can fail and either cause not enough power or too much power to be passed through.