You asked, so here are my $0.02

. Like most things in life (at least in my xp) the answer isn't yes/no, it's a grey. I think it's fine under the vast majority of circumstances. I assume you're talking about laptops since you mentioned power supplies, but if not then this list of possible bad endings will be smaller.
Devil's in the details though: Are you plugging it in to charge it (e.g. battery installed)? Is the circuit close to being overloaded already? Is it in a janky extension cable? What kind of circuit overload protection is installed at the charging location/residence? What kind of charger are you using? (e.g. OEM Apple vs. off-band) Is the charger ETL/UL listed/certified? How old is the wiring in your residence? Etc =)
I can only brainstorm 3 plausible disastrous outcomes:
1) Battery explosion/fire due to faulty charging circuit/software (if fitted)
2) Laptop overheats/shorts out/catches fire (if running)
3) Power supply fails and explodes/catches fire/shorts out
So if you have a battery you trust, an OEM charger in good physical condition, and you're laptop isn't on and is well ventilated I think your odds of having something go sideways with your PPC are negligibly higher than having your cell phone/new laptop plugged into the same circuit where you sleep.
If in doubt, unplug it!!