Center pin negative? Or the center plug?

*REMEMBER* Center pin must be positive. Incorrect polarity will damage the module and may result in personal injury.

The center pin must be NEGATIVE (no, not positive, as the warning reads). So, the correct warning should read:

*REMEMBER* Center pin must be NEGATIVE. Incorrect polarity will damage the module and may result in personal injury.

We regret any inconvenience this may have caused.

fail. GTFO