Without looking at Griffdowg's reference to see if I am duplicating -
Western mainland Europe, Scandinavia, Russia, Baltic States (probably also all other South Eastern European countries) now uses the European system of 2 pin system of wall sockets. Same voltages too.
However this is a fairly recent development.
Before Perestroika, which opened up international markets to former USSR states, Russia used a similar socket/plug but with a slightly smaller diameter pin. The matching sockets, unless the plastic is worn or broken, will not quite allow a 'Euro' plug to fit in.
There are a number of older or unmodernised buildings still using the older style smaller pin size socket. These tend to be homes rather than business premises.
I wouldn't worry too much about this.
Wherever the old sockets are still installed, the owner will have small cheap (50Eurocent) adapters. All electrical appliances, leads etc, for the last 20+ years come fitted with Euro plugs - and this was the period of spectacular consumerism compared with the past in RUS, so every single person will have bought appliances with the Euro plugs even if not upgraded their sockets.