I'm going to go against the norm here. It's probably better to have them plugged in sometimes, if not always. Old capacitors can dry out and become brittle, which can destroy a mainboard when they surge and pop.

Nothing you do will be 100% guaranteed to keep electronics alive forever, because components wear out. Each console will have specific components with specific failure types that means that some are better having always power, some are better with sometimes power, and some are better with zero power. But my gut says that older consoles plugged into a quality UPS will probably last longer than a console sitting in a box unpowered.

https://en.wikipedia.org/wiki/Capacitor_plague

This is just one type of failure mode, but there are many other things that can cause damage. Power surges, transformer enamel wearing out, resistors cracking, thermal cycling of solder, thermal paste drying out, permanent CMOS batteries dying.... etc. etc. etc.

Let's be honest, old consoles were BEASTS.

I remember my old PS2 used to be perpetually on, I would come home and just flip on the tvand there was my game, sometimes it was a neccesity if I was playing a ps1 game because I didn't have a ps1 memory card, I swear that thing had to be on for months at a time and it was just fine.

It gets a little harder the newer the console is though, take the 360, if I had done that with that console it would be red ringed before a week Take this with a grain of salt of course, if you wanna be safe, then yeah go ahead and keep it unplugged, or better yet, get a power switch so all you have to do is hit a button, but that was my experience

Ignoring something like a power surge, it's fine. There's no standby mode, and there's no "ebs and flows" of current on an open circuit like another comment suggests.

If you're not gonna use it for a few years, unplug it just in case one of those power surges we are ignoring happens.

Like all things, don't shelve them for a long time... degradation will get to them eventually. Like laptops and tablets, at least once a month or so fire it up to get it working.

"Wall warts" AKA AC-to-DC adapters do draw a small amount of electricity as long as they are plugged in. Unplug them when not in use.

As for the consoles, capacitors dry out and go bad even when not in use. If you power up the console at least once every few years, it is possible for the caps to "re-form" and stay useful before needing replacement.

Sadly, my previously working PS2 no longer outputs audio or video after being in storage for a few years. I haven't had time to investigate it further, but I have had several other pieces of quality Japanese electronics go bad after their supercapacitors leaked.

I'm just gonna go out on a limb and say that leaving them plugged-in indefinitely is not good for them.

I am not an expert but with limited knowledge, power going into your devices isnt uniform depending on what's being used in your home.

So these ebbs and flows of current into your devices will wear out the electrical components over time.

I'd say unless you play retro games regularly, keep the consoles unplugged until you decide to pop a cartridge in.