ballast types?

How do you tell what type of ballast you have if its a S51 or what. I have a 400 watt electronic switchable ballast but it does not say. I dont want to get the wrong type of bulb and it not work. Cause Ive seen bulbs on ebay that say for a S51 ballast.

So from what I see an S51 ballast is a magnetic ballast right? So can I use a bulb Made for a S51 ballast in a electronic ballast?

it says a s51 is hps and switchable tells u that u can run hps or mh bulbs what is namebrand of ballast and any other specs