[NicknamedBob]

"I thought it's dangerous to open those power supply boxes, or is it not?"

Step number one. Power down the unit. Stare at the disconnected plug in your hand for several seconds.
... Step one A -- see below.

Step number two. Know what capacitors look like and avoid them. They bite!

Step number three. Touch nothing inside with your own flesh.

Step number four. If you don't have the tools, materials, training or patience to follow these rules, go to step one A. -- Throw it out and buy another.

[Baraonda]

I think I'll throw them boxes away.

Better safe than sorry.

[sionnsar]

go to step one A. -- Throw it out and buy another.

Glad we didn't have to. The 26 year old microwave goes well with the 52+ year old toaster.