This is a small DC/DC converter. It converts +5V DC to -30V DC, with an output current of a few mA. Check the "documentation" link for the hookup diagram. A quick test gave these results: with two 100k resistors as loads -33.0V and -28.8V with 10k -31.25V and -27.5V with 2k2 -25.7V and -23.0V.
This is a surplus product. It was obtained from a surplus store, from an inventory or from any other secondary source. You can expect this product to be in good working condition, but it can show signs of being handled, shipped, repackaged etc. The supply of a surplus article can suddenly run out, or the price can change. Get it while it is available.