Measuring Power per Hertz of a RF signal
While "-50dBm/Hz" can be interpreted as "with 1 Hz RBW, no point exceeds -50dBm", it is generally expected that your signal power is somewhat evenly distributed over the entire bandwidth. Thus, it means that your transmit power maximum is this value times the transmission bandwidth, i.e. for 1 MHz bandwidth, you get +10dBm.

However, that assumes ideal distribution of power, which you hardly ever get, so that is a purely theoretical value. What is practically possible depends to a large extent on the scrambling algorithm you use.

The regulations should also specify how compliance is tested -- typically with an RBW of a few kHz, VBW > RBW, peak detector and a fairly long sweep time.

Measurements with an RBW of 1 Hz are not really useful in compliance tests, because they take ages and see only little of the actual signal power.