bitrex wrote:

I have a used Dell Inspiron 5558 laptop, which didn't come with an OEM
power supply. I picked up a 65W "universal" type for it off Amazon, and
it's showing some weird behavior.

I'm not surprised.

Dell laptop power supplies have a 3rd "sense" wire (a pin in the centre
of the coaxial barrel) which allows the laptop to identify whether a
genuine Dell charger is being used, and without one it is likely to run
at low CPU speed, and refuse to charge the battery.

Look on ebay for an appropriate PA-series, what model laptop do you have?