Debouncing a pushbutton switch
 

I try to avoid equipment fitted with mechanical push-on push-off mains switches, which were popular in the 60s and 70s until manufacturers realised they were destined to fail and repairers realised they cannot be repaired with all their little wire and bronze springs and stamped paxolin bits. Once you've got a bit of processing onboard you can fit a simple push-to-make switch; for the power switch this will be a simple on-off function but multiple 'way' functions can also be implemented.

For some time I've been using a fairly basic monitor speaker for the everyday laptop and been forever frustrated by the absence of any debounce provision made by the manufacturer so it has needed about 5 pushes on average to switch it on. We all know that 10nF across the contacts usually cures this so I added one, which not only cures it but has the unexpected benefit that as soon as you switch on the mains for PC + monitor the monitor switches itself on. Bear this in mind if you specifically need the device not to start 'on'

Re: Debouncing a pushbutton switch
 

is the switch switching mains, or DC?

If it's switching DC then something using a 555 and a reed-relay would be my preferred approach.

Re: Debouncing a pushbutton switch
 

All the works are fed from the mains transformer so it's switching DC with a small transistor or MOSFET, no point in replacing that with a relay. My 'timer' is smaller than yours and uses only one component!