As was mentioned before, all LEDs that run natively on 12VDC are dimmable with the cheap PWM eBay dimmer linked before. An LED is perfectly happy with the high-frequency pulsing of the PWM dimmer.
It is the 115VAC ones where not all are dimmable. This is because the internal power supply is a tiny switching power supply and needs to be a bit more complex in order to deal with an input power waveform which is not the standard full-voltage sine wave. If you try to dim a non-dimmable 115VAC LED you will likely get flickering, a hot power supply and short time-to-failure.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam
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