False triggering of IR receiver

I am using IR LED in my circuit. Ready-made 12V DC switching supply is used. I have noticed that IR receiver produces pulses without any signal. When switching supply is replaced, the false triggering of IR receiver stopped. There is no any ripple or noise in problem switching when observed by oscilloscope. Filter capacitor of 10M and 47R resistor are used at IR pins accordingly.

What may be wrong with faulty switching supply?

It's normal, lots of stray IR in a typical room. Try putting your hand over it and see if the problem goes away. If so you'll need a way to filter it.
PS IR detectors like the TSOP1138 and such are 5V devices.