Im using the P50 and felt it made a difference to my sound. It also has more than enough power even when running both USB slots, one for the Wiim Pro Plus and they other is running a fan to cool my amp. No issues with lack of power supply at all.Well I should receive my topping p50 tomorrow and so I'll be testing this. The p50 has 2x 5V/1A usb ports, and I intend to use both at the same time.
Those power draw numbers you mentioned for the WiiM sound right, so even though the team officially recommends a PS rated at 5V/1.5A minimum, I think it will be ok.
Max 0.9A draw from the WiiM Pro is manageable for the p50 imo. Guess I'll fond out if there are any performance issues!!