Lowering the power limit isn't the same as undervolting. Lower the power slider limits the max power the card is allows to draw, which it achieves by adjusting the clock frequency. This will override the frequency setting (which sets the max frequency the gpu is allows to run up to, if it's power target allows) so... yes it's safe but it won't improve performance.
Undervolting means adjusting the voltage the gpu is set to run at - say a particular gpu is set to normally run at 1.2v by default, this value is set by the manufacturer based on what the average chip is stable at, if you have a good quality chip then it may run at say 1.15V without issue. The advantage of lowering the voltage is that at a given frequency the gpu will produce less heat which may actually allow the gpu auto boost functionality to run at a higher boost state (or hold the boost state for longer). Undervolting should be fairly safe as if anything lowering voltage will put less strain on the gpu however if you lower it too far the card will become unstable and might crash so it's worth adjusting in small steps and testing to make sure the card is still stable.
Edit: Also I'm not sure if you will gain much by undervolting a GTX 1650 - it became a hot topic with the AMD Vega 56 and Vega 64 gpu's as AMD set a very high default voltage on those cards from the factory so most users found their cards ran better at lower voltages. I haven't heard much about undervolting on the GTX 16XX cards so you might find the card will simply become unstable if you lower the voltage.
Undervolting means adjusting the voltage the gpu is set to run at - say a particular gpu is set to normally run at 1.2v by default, this value is set by the manufacturer based on what the average chip is stable at, if you have a good quality chip then it may run at say 1.15V without issue. The advantage of lowering the voltage is that at a given frequency the gpu will produce less heat which may actually allow the gpu auto boost functionality to run at a higher boost state (or hold the boost state for longer). Undervolting should be fairly safe as if anything lowering voltage will put less strain on the gpu however if you lower it too far the card will become unstable and might crash so it's worth adjusting in small steps and testing to make sure the card is still stable.
Edit: Also I'm not sure if you will gain much by undervolting a GTX 1650 - it became a hot topic with the AMD Vega 56 and Vega 64 gpu's as AMD set a very high default voltage on those cards from the factory so most users found their cards ran better at lower voltages. I haven't heard much about undervolting on the GTX 16XX cards so you might find the card will simply become unstable if you lower the voltage.