This paper presents evaluation of quasi-resonant flyback (QRF) dc-dc converter 57 W with valley-switching in an emerging application. The QRF was supplied from an 800 V variable dc-link and was used as the auxiliary power-supply of a wireless inductive-charging system (ICS). Comparison of stateof-the-art QRF control ICs is presented and suggestions for their improvements are given. Notes on the power-supply architecture, design items specific for the ICS application, over-power protection, and keycomponent choice are provided. During experiments several original and novel results are generated. The efficiency graphs in ICS power transfer, ICS stand-by, and constant-load operation are analyzed. The maximum efficiency of 87.1 % was reached at 620 V and rated load. Moreover, the unique analysis of QRF losses at no-load, showed their quadratic dependency vs. input-voltage. The measured "switching frequency vs. load" graph is presented. It was changeable with load and input-voltage as expected. From Bode plots the bandwidth, phase-margin, and gain-margin are extracted and plotted versus input-powerfor the first time. They were changeable with input-voltage and load as expected. Comparison of simulated and measured Bode plots showed that, even when they were not matched, one can design a Type-2 compensator that ensures stable operation. Evaluation of cross-regulation, when output with 24.1 % of total power was regulated, showed that such approach-contrary to the more common of regulating the biggest one-is feasible too. It is discovered that, for a QRF with variable switching frequency, choice of compensator or the regulated output has influence on its efficiency. The power-thresholds to ensure valleyswitching operation represented as "input power vs. input voltage" are shown for the first time. Comparison of bandwidth, phase margin, and gain margin vs. input power, between an ACF and the QRF, were discussed. Conclusion is that QRF, for the same specification, cannot have the same compensator as an ACF. The difference must be at least in a placement of a zero.