When you made the change to 500 Hz, did you also change the size of the LC
filter network?

500 Hz is 200 times lower which will necessitate much different filter
components.  The filter network is designed to only store energy for the
period of the pwm. If you did not change the size of the network, it can
only handle a period of 10 usecs (100KHz). At 500 Hz, you have a period of
2 milliseconds (200 times longer) so you will need filter components much
larger. Your dmm may read the average current correctly but it is the peak
current that is causing the wall wart to get hot.

Tom M.

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