That 2YK0F 65W Liteon power adapter was never validated for the Latitude 5420. Go back to using the VT148 65W Liteon power adapter that shipped with your Latitude 5420. The Latitude 5420 is only validated with the following OEM power adapters =22TH3 90W DeltaR2M8K 90W LiteonWMDHR 65W ChiconyCDH54 65W DeltaFTTTJ 65W DeltaVH2W4 65W HuntkeyGJJYR 65W LiteonVT148 65W Liteon
I'm wondering if Dell has specifications regarding how hot the laptop power adapters are allowed to get before they are considered defective? The  power adapter that came with my 5420 operates at a relatively cool 120 degrees F, even when it's charging the battery from a low percentage and operating the laptop at the same time. I like the previous generation style adapters, and I found a "genuine Dell" 65W USB-C power adapter on Amazon, so I got it. I closely inspected it before I plugged it in, and it seems to be genuine. When I plug it into the laptop, after a half hour or so it gets really hot- like 155 degrees F. The adapter is a HA65NM170. Is that temperature within spec?
Latitude 5420, AC adapter, how hot is too hot?