DC test equipment to see voltage extremes?
There exist many DMMs with peak detecting capabilities, some for less than $50. Just look for those that have a Min/Max setting or button.

These are not as fast or versatile as a more expensive oscilloscope, and you should check the specifications to learn how small of a peak these can measure, but these should be much more than enough to satisfy your needs.

The more expensive ones advertise Fast Min/Max which can detect peaks shorter than 300µs.