There is a reason why there are so many sulfur masks on the market, they are extremely effective at kicking adult acne to the curb. Here are a few of the sulfur masks (and spot treatments) that can amp up your anti-acne routine and make it far more effective than ever before.

Another brand with a very well-deserved good reputation is DDF. The editors of Allure magazine chose DDF's Sulfur Therapeutic Mask as one of there favorites and it has also been recommended by Sephora to me repeatedly. The mask has the same 10% sulfur kaolin and aloe that the PTR mask has but there is no need to use a separate product to get the soothing allantoin. This may be a better choice for some people wanting to use it as both a mask and a spot treatment and it and the PTR cost exactly the same. This one is currently on backorder directly from the manufacturer. I recommend trying to get it (and any other products you can) from Skinstore.com anyway and using the promo code "FAB20" to get 20% off your order.
For those who are big fans of Proactiv, their Refining Clay Mask is truly the best product they make. While is does not have as high a concentration of sulfur as the previous two (it has only 6%), it also has kalin and some omegas to help heal the skin and get rid of acne and is far less expensive. It has also been recognized by Allure Magazine as being one of the "Beast of Beauty" products.
Though Philosophy has already discontinued their "On a Clear Day" line and replaced it with the "Clear Days Ahead" line, Philosophy devotees looking for an anti-acne product with sulfur can snap up some of the last remaining On a Clear Day Oil Free Acne Spot Treatment. With 3% sulfur, salicylic acid and a peptide aimed at helping to heal blemishes. Also as far as spot treatments go, It (and the PTR one mentioned above) are two of the few sulfur spot treatments with no tint which is a really good thing.

A similar product to the Kate Somerville, but with an added tint (which can be a huge negative if your skin tone doesn't match) that costs a few dollars more is EmerginC Tinted Blemish Control Drying Lotion. This one also has minimal ingredients, but doesn't specify the concentration of sulfur in the product. For someone wanting a similar product that is vegan and/or GMO-free, look into Dr. Dennis Gross Acne Clearing Lotion with Trifix.
Some other options are Origins Out of Trouble Mask, Clearasil Adult Tinted Treatment Cream and Dermalogica's Concealing Spot Treatment.