We also have PlayStation®Network Cards for our PlayStation®Wallet
There is a distinction. SEN is geared if you don't own a playstation device. Sony does makes other products, not just play stations.
People who don't own a playstation will use SEN.
Actually what we are using is now SEN. Many people say PSN because they're used to saying it. PSN was what SEN is today before Sony decided in 2012 that they wanted to support it's eco-system to other devices and have PSN renamed to SEN and treat PSN as it's videogame network within SEN.
SEN is basically,
etc for any third parties and such
all in one.
It'll distinguish what service can be used by the hardware it logs on.
“I might have laughed, if I had remembered how".– Max Payne