Varistor and TVS diodes in series
An MOV is not the same as a TransZorb. An MOV has a soft avalanche while TransZorbs have a sharp zener-like cut-off. Both are transient absorbing devices.
For constant voltage clamping zener diodes are better suited. In terms of protecting power supplies it is best to put MOV's or TransZorbs  or RF noise filter capacitors (1 nF X2 rated)on the AC side of the diodes. Zener diodes, if used, would be installed after the rectifier diodes.
I worked in the TVS / SPD industry for 15 years, and putting devices in series was common. They are more balanced than you think. As they do not make individual units (so far) with a rating over 1,200 VAC, to protect 4,160 VAC oil-pump motors we put 4 or 5 in series, then several of those in parallel to get the KA rating required by the vendor, and the safety margin required by UL and ISO.