great for lowering the power of the rw8 which was to strong for my tank but still allows me to keep the rw8 if I should ever wish to upgrade. I must add that it is VERY silent in its operation.

Do a verry good job if you have to mucth power with WP pump !

It is a great commodity.
I recommend!

I really like this unit! I can control my wp-40 with it. I don't use the night sensor on the pump, I found just turning the volume on the pump makes the red light come on, so adjusting the voltage slightly solves this. I am generally around 19 volts

This power supply is an excellent solution to reduce speed and also noise for the WP jebao pump. I adjusted it to 18V for my WP10 and it work perfectly for the size of my tank.

I ordered two WP-40 pumps and they came with the standard power supply. In my opinion the pump with the standard power supply is noisy in wave modes. I purchased two of the adjustable power supplies, have them set at the 19 volt setting and my pumps are almost silent.
The adjustable power supply also reduces the output of the pump so if you have a smaller tank this will work for you.
Bottom line is if you are going to buy the WP-40 you should also buy the adjustable power supply.

I purchased a wp40 but it had too much flow for my 4' 120g tank. But when they came out with the voltage controller I immediately ordered 1 . Works awesome , a must for these pumps with way more variety of flow in your tank so you can dial it right in . I loved it so much , I ordered another pump & can't wait till the wp25 comes out !!!