As mentioned above, the power "brownouts" where there is low voltage are caused by too many people being hooked onto a single transformer. Installing your own transformer should fix the problem, but is rather expensive. Installing voltage regulators can help as well, but then you are paying for additional power because the regulator is not 100% efficient.
Currently we don't have low voltage problems at the west end of Cabarete. Power is on for 9 hours and off for 3 and has been for some time and even roughly agrees with the schedule posted on the Endenorte web site:
EDENORTE DOMINICANA S.A
This means inverters are still needed to bridge the gap ( or a generator). We have been promised 24/7 power as well and are told we are on the list to get it soon, whenever that is.
Regarding the internet speed. This may have to do with how far you are from the central station and may be due to the quality of the line. It also depends upon the level of service for which you are paying. We had a problem where I noticed the speed had dropped. I called service and they replaced the twin lead wire with a coaxial cable ( similar to what cable TV used) and the speed rose dramatically. So you might want them to check that.
If you are somewhat technical, you can check your DSL modem's connection integrity. Try typing 10.0.0.1 into your web browser. This works for most Speedstream modems and is the modem's address. If you get a response from your modem, go to Status and Statistics on the left side of the page and then choose DSL. A table with many entries will no be visible. There is a heading called SNR. This is the value of the Signal to the Noise on your connection as measured by the modem. If it is in the 20's you are OK. My SNR is about 28.5, for example. If it gets into the 10's you have a connection problem that might be due to a bad quality of wire or connection.