In recent years, many advanced control strategies have been proposed for wave energy converters (WECs), which significantly increase the energy conversion rate of the devices. So far, most of these control schemes have only been investigated theoretically using simulations, which, to a great extent, are based on idealized assumptions. On the contrast, far less information regarding the testing of these control schemes in experimental setups can be found. Under such circumstances, the control performance might be compromised by many factors such as model uncertainties, measurement noise, or delay. This paper compares the performance of a spring damper control and an advanced control strategy for a point absorber WEC in wave tank experiments. For two different irregular sea states, the energy conversion of the advanced control, which uses an observer to estimate the wave excitation force, is compared to the performance of a spring damper control. The results show that, with the advanced controller around 13%-14%, more energy could be converted when compared to the spring damper control. Additionally, the observing process was found to be critical in the advanced control. The conducted experiments show that an increase in the observer accuracy holds a theoretical potential to further improve the energy conversion rate by 15%-25%.