Meter by itself will work fine; I've tested a couple this way. Keep in mind that on the original units you won't see 5Vdc on the output. You'll see your meter go to 12Vdc (or whatever the input voltage is) and stay there until the internal coil heats up. After a a minute or so, the meter will start showing the output switching on and off to provide an approximate average of 5V. You can add the capacitor and see that it will slow down the movement of the needle on your meter (if the cap is working correctly) as the regulator switches on and off.