There is a diagnostic technique common to everyone who owns a 3D printer, and it goes like this: wiggle the wire, squint at it, and announce "yeah, I think it's getting power." That is not a technique. That is a prayer with extra steps.
I lost most of a weekend last winter to a printer that kept rebooting mid-print. I checked the firmware. I reflashed the firmware. I insulted the firmware out loud, to nobody in particular. It turned out to be a crimp with about four strands of copper heroically doing the job of twenty, which a continuity beep would have found in eleven seconds.
The actual spec sheet part
This is the DT830B, which is more or less the meter people picture when they picture a multimeter. DC voltage up to 1000V, AC voltage up to 750V, DC current to 10A, resistance, diode test, transistor hFE and a battery check, all on a single rotary knob. No menus. No two-button combination to remember at midnight.
It has a 3.5-digit LCD, overload protection on the ranges, runs off one 9V battery, and ships with probes. It is roughly paperback-sized and weighs approximately nothing, which matters when the thing lives in a drawer instead of on a bench.
Why it's actually useful here
If you own a printer, you own a small pile of wiring that will eventually lie to you. Checking whether your PSU is really delivering 24V or has quietly drifted south. Continuity-testing endstop and thermistor runs before you start blaming the board. Confirming a heater cartridge has not gone open circuit. Measuring resistance across a stepper coil before you accuse an innocent driver. Working out which of the six identical black wires in your salvage drawer is the one you actually want.
It also settles the eternal household question of whether that USB brick in the junk bin is dead or merely sulking.
It holds a 4.9-star rating across 5,506 reviews and more than 10,000 orders, which for a meter that costs less than lunch is faintly ridiculous. My favorite review is from someone who says he has thrown away roughly ten expensive brand-name meters over the years and never one of these, largely because this one takes a 9V battery instead of the AAAs that leak and quietly destroy the instrument around them. Check it out here, and may your next mystery reboot take eleven seconds instead of a weekend.