6П3С-, 6N3С-, and 63PS are three terms for the same type of vacuum tube (valve in Bristih English). 

The reason for the different names is that it's a Russian-made tube, where some are labeled with Cyrillic letters, by some producers and writers converting the Cyrillic ø П ‘ to a ‘P’ (which is the closest letter from Russian to English) or an ‘N’, which looks the most similar to the Russian ’П’ letter.

Many tubes in the same family - often under both Russian and American/English family names

If you want to add further confusion, 6П3С-, 6N3С-, and 63PS tubes are related (sharing characteristics in different domains) to the following tubes: 3108_OSW; 6L6G; 6L6GA; 6L6_DDR; 6Л6С; 6П3; 6П3С-Е; OSW3108 - which to varying degrees are equivalent to the corresponding American tube series in the 6L6 and 5881 families.

The 6П3С-, 6N3С-, 63PS- was popularized more broadly 10-20 years ago at a time when prices of 5881 and 6L6 tubes from American manufacturers like Tung-Sol, RCA, Sylvania, and General Electric skyrocketed due to simple supply and demand.

These output tubes are used in both guitar amplifiers and hi-fi products (my own experiences come from using them in an Audio Note P2SE (fraom Audio Note UK, not Audio Note Kondo) power amplifier in addition to my current Leben CS-600, which came from the factory with four pieces of 5881/6l6WGC tubes.

The Leben CS-600 is compatible with a wide range of different output tubes. For a chart of settings and supported tubes, see this blogpost: The Leben CS-600 Amplifier ~ Photos, Tubes, Impressions.

I recently bought a closely symmetrically measuring set of 6П3С, 6N3С, 63PS and two sets of the successor Tube of the Week: 6П3С-, 6N3С-, 63PS-E.

The picture shows a 6П3С tube produced in the 70s by either Reflector or Proton (in Russia).

For further reading / more information about 63PS and 63PS-E tubes, I can recommend the overview pages for each tube on Radiomuseum - they can be found under 63PS/6П3С and 6П3С/63PS-E respectively.

Each link contains pictures of the tubes, datasheets, and a 'cross-navigation section' to tubes in the same family, both in the Russian and American 'family', which is a convenient way to understand the genealogy.

Even though the tubes look very similar, if not identical, and the sockets match, it’s important make sure they’re compatible in terms of electrical variables as both the tube can be easily damaged, but also, in some cases, permanent damage might be caused to the amplifier.

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