Hope someone could give me enlightenment on this one:

I use a standard 9v DC adapter for all my pedals - I've checked the voltage, polarity - its all good. My pedals work perfectly fine when plugged into a battery operated amp/amp with small voltage (e.g. below 10v), but once its plugged into a larger amp (with higher voltage), or into a soundboard/mixer, the power adapter just doesn't work! It happens on multiple amps, with multiple pedals (I've tried with 4 different guitar and bass pedals and got consistent findings). I can see the pedal power-on light simply go off once I plug the output cable into the amp (even when the amp is turned off).

I'm really stumped by this one - the only possibility I can think of is that it has to do with the current, but then again I don't know much about electronics. Is this "phenomenon" normal? Please help! I've ended up using the battery option for my pedals but sometimes disaster strikes and the battery runs out in the middle of a gig (due to my own carelessness I admit).

p.s. I hope this is in the correct category
Meaning your pedals work with some amps and not with some others?
That's not normal at all.

Are you connecting the amp and pedals to the same power outlet?
This is bizarre. It's as if the DC side of the power supply is not isolated from the AC neutral. You could use an ohm meter to check. I'd suggest trying another supply.
Thanks for the replies!

My pedals work fine on battery power, but for power supply they only work if I use my 3w amp or if I plug my headphones straight. Just can't work on my 20w and 30w amps and above. I'm connecting the pedal power supply and the amps into the same multiplug would that cause the problem?

I'll try to use another power supply I guess... just gotta search around the house haha.