AC voltage on a DC power supply?

[iamashwin99]

I was using my old routers power supply to light up an led strip with a simple LDR based night detector. When I was assembling the setup, I felt a strong tingling sensation when I touched the power supply. I took a multimeter and found out that it measured 10.2V in DC setting and about 15V in the AC setting. Troubled by this reading I switched to a cheap LED strip PSU and this too measured about 12VDC and about 20VAC.
My question is whether this is a normal behaviour or something going wrong?

Interestingly my 2n2222 based night detector worked for one day and stopped working from the next time I turned it on. Could the AC voltage destroy it? I'm thinking of adding a relay to output the power to leds rather than a direct connection from the transistor. Should I try building a low pass filter before the input to the transistor?

[HB9EVI]

Without further infos to the PSU just guessing. what type of supply is it? old transformer based supplies often just had a rectifier and a cap but no voltage regulator; a smps could have an isolation problem between the primary and secondary side, some more infos would help